401 Error: What It Means and How to Fix It

A 401 Error occurs when a server cannot verify your identity because it didn’t receive valid authentication credentials for the requested resource. This can happen when authentication details are missing, incorrect, expired, or otherwise unable to prove your identity.

Encountering a 401 Unauthorized error can be frustrating, especially when it locks you out of a page or resource you badly needed access to. Fortunately, the issue is often easy to fix. Depending on the cause, you may need to review authentication details, clear stored browser data, or check website and server configurations.

In this guide, you’ll learn what the error means, why it happens, and how to fix it.

What is “401 Error” (Unauthorized Access)?

A 401 error code indicates that a server cannot verify the identity associated with a request because it didn’t receive valid authentication credentials. Unlike a 403 Forbidden error, which occurs when a user is recognized but denied access, a 401 error occurs when the server cannot verify a user’s identity.

This error can occur when attempting to access login pages, member-only content, admin dashboards, APIs, or other protected resources that require authentication. In most cases, you can resolve the issue once you identify the underlying cause, whether it involves login credentials, authentication settings, or other factors affecting identity verification.

Depending on how a website or application is configured, users may see different variations of the error message, each providing clues about the specific authentication issue involved.

What Are the Variations of 401 Authentication Error?

When a 401 Unauthorized error occurs, browsers and applications may display different error messages, such as:

• HTTP Error 401
• 401 Authorization Required
• 401 Unauthorized Error
• Access Denied
• Unauthorized

While the wording may vary, these messages generally indicate the same underlying issue: the server could not verify the user’s identity because it did not receive valid authentication credentials.

Websites running on Microsoft Internet Information Services (IIS) may provide additional details through sub-status codes. These codes are specific to IIS and aren’t part of the HTTP standard, so Apache, Nginx, and most other web servers won’t show them. If your site runs on IIS, the table below can help identify the root cause.

401 Sub-status Code	Meaning	Description
401.1	Logon failed	The authentication attempt failed because the username, password, or other login credentials provided were invalid.
401.2	Logon failed due to Server configuration	A problem with the server’s authentication settings prevented the system from validating the user’s credentials.
401.3	Unauthorized due to access control settings	The server denied access because file, folder, or resource access-control settings restricted the requested resource.
401.4	Authorization failed by filter	A server filter or security component blocked the request because it failed an access or authorization check.
401.5	Authorization failed by ISAPI/CGI application	An application running on the server rejected the request because of an authentication or access-control issue.
401.501	Access denied due to concurrent request limits	The server denied access because it received too many simultaneous requests from the same IP address.
401.502	Access denied due to maximum request rate limits	The server blocked the request because the number of requests from the same IP address exceeded a configured rate limit.
401.503	Access denied due to an IP address restriction	The client’s IP address appears on the server’s deny list and is not allowed to access the requested resource.
401.504	Access denied due to a hostname restriction	The client’s hostname appears on the server’s deny list and is blocked from accessing the requested resource.

Website visitors do not always see these codes on the error page itself. They are more commonly found in web server logs, hosting control panels, application logs, or developer tools.

What Are the Causes of a 401 Error?

A 401 error can occur for a variety of reasons, ranging from incorrect login information to misconfigured authentication settings. Although the specific cause may differ from one situation to another, the underlying issue usually involves a failure to verify a user’s identity or authentication details.

Below are some of the most common causes readers may encounter.

• Incorrect or invalid credentials: The server cannot verify a user’s identity when an incorrect username, password, API key, access token, or other login information is submitted. Even minor typing errors or expired credentials can trigger a 401 Unauthorized error.
• Session timeout: Many websites automatically end inactive sessions to protect user accounts. If a user attempts to access a protected resource after the session expires, the server may reject the request because the associated authentication token is no longer valid.
• Faulty authentication methods: Problems with authentication systems, login integrations, identity providers, or token validation processes can prevent the server from verifying a user’s identity. If the authentication scheme fails, the server rejects the request and returns a 401 error.
• Outdated browser cache and cookies: Stored browser cache and cookies may contain outdated or corrupted authentication data that no longer matches the current session. This can create conflicts that prevent the server from successfully validating the request.
• Plugin incompatibility: Certain plugins, especially ones relating to security, membership, or authentication, may interfere with login processes or access controls. In some cases, plugin conflicts can mistakenly treat legitimate users as unauthorized and deny them access.
• Misconfigured .htaccess file: Incorrect authentication rules, access-control directives, redirects, or password-protection settings within the .htaccess file can prevent legitimate users from accessing a resource. These misconfigurations may cause the server to reject requests that would otherwise be valid.
• Incorrect URL: An incorrect, outdated, or bookmarked URL may lead to a requested resource that requires authentication. If valid credentials are needed to access that page, the server may respond with a 401 error.
• Server or authentication configuration issues: Problems with server-side authentication settings, access policies, user role mappings, or identity verification systems can prevent the server from validating legitimate requests. As a result, users may encounter a 401 error even when they believe they are using the correct credentials.
  

Although these causes vary, they all stem from the server’s inability to successfully verify authentication information. Understanding what triggered the 401 Unauthorized error is the first step toward resolving the issue.

401 Unauthorized Vs 403 Forbidden

A 401 Unauthorized error is commonly confused with a 403 Forbidden error because both prevent users from accessing a webpage or resource. The key difference is why access is denied. A 401 error means the server cannot confirm who you are, while a 403 error means the server knows who you are but will not allow access to the requested resource.

401 error asks “Who are you?” while a 403 error simply says “I know who you are, but you can’t access this resource.”

Understanding this distinction can help you identify the appropriate troubleshooting steps and resolve the issue more efficiently. The table below compares the key differences between 401 Unauthorized and 403 Forbidden errors.

Factor	401 Unauthorized	403 Forbidden
What it means	The server cannot verify the user’s identity.	The server recognises the user but denies access to the requested resource.
Root cause	Missing, invalid, or expired authentication credentials	Insufficient permissions or access restrictions
Authentication status	Authentication failed or is required	Authentication may have succeeded
Common examples	Incorrect password, expired login session, invalid API token, or missing access token	Restricted admin pages, role-based access restrictions, blocked directories, or insufficient user privileges
How to fix it	Sign in again, verify credentials, renew authentication tokens, or review login settings.	Request access, review user roles and permissions, or contact the website administrator.

How to Fix a 401 Error

You’ll have a much easier time fixing a 401 error once you’ve identified what’s causing it. In some cases, the solution may be as simple as checking your account details or signing in again. In others, you may need to review website, security, or server settings. The troubleshooting steps below cover the most common fixes for both website visitors and administrators.

Fixes for Website Visitors

If you encounter a 401 error while accessing a website, start with the simplest troubleshooting steps first. Many authentication issues can be resolved by verifying login information, refreshing your session, or clearing outdated browser cache and cookies before moving on to more advanced checks.

• Verify the URL: Confirm that the web address is correct and does not contain typing errors, outdated links, or unnecessary characters. An incorrect URL may lead you to a resource that requires authentication.
• Check your login credentials: Verify that your username, password, API key, or other login information has been entered correctly. Invalid or expired credentials are among the most common causes of a 401 Unauthorized error.
• Log in again or reset your password: If your session has expired or there is an issue with your account, signing in again may re-establish authentication. If you’re unsure whether your credentials are correct, resetting your password can provide a fresh start.
• Clear cookies and site data: Outdated or corrupted browser cache and cookies may store authentication information that no longer matches the current session. Clearing this stored browser data can help create a fresh connection between your browser and the website.
  

Fixes for Website Owners and Administrators

If the issue extends beyond a single user or persists after basic troubleshooting, then you may need to review website, security, or server configurations. The steps below can help website owners and administrators identify and resolve common 401 error causes.

• Check whether the affected URL should require login: Verify whether the affected page, directory, or protected resource is intentionally restricted. In some cases, authentication requirements may have been applied incorrectly, preventing users from accessing content that should be publicly available.
• Test with a valid user account and review authentication logs: Try accessing the resource using a verified account to determine whether the issue affects all users or only specific accounts. At the same time, review authentication logs and server logs for failed login attempts, invalid tokens, or other authentication-related errors that may reveal the root cause.
• Disable WordPress plugins temporarily: Security, membership, and authentication-related plugins can sometimes interfere with login processes or access controls. Temporarily disabling plugins can help determine whether a plugin conflict is contributing to the error.
• Review .htaccess authentication rules: Examine the .htaccess file for incorrect authentication directives, password-protection settings, redirects, or access restrictions. Even a small configuration error can cause the server to reject legitimate requests.
• Review website security settings: Firewalls, IP restrictions, security plugins, and other access-control mechanisms can sometimes flag legitimate requests as suspicious. Review your website’s security configuration to ensure protective measures aren’t unintentionally blocking authorised users.
• Check API credentials and authorization headers: If the error occurs when accessing an API, verify that API keys, access tokens, and authorization headers are present, valid, and up to date. Expired credentials, missing bearer tokens, or incorrect implementation can prevent successful authentication and trigger a 401 response.
• Confirm user roles and permissions: Strictly speaking, permission problems should return a 403 error, but some applications and plugins return a 401 instead. If valid credentials are still being rejected, review account roles and access privileges to make sure users have the right level of access.
  

Preventing a 401 Unauthorized Error

While you can’t prevent every 401 error, proactive management of authentication and access settings can help reduce the risk of access-related issues. Below are some best practices for preventing 401 Unauthorized errors.

• Implement strong and secure authentication mechanisms: Strengthen your login process with strong password policies, multi-factor authentication (MFA), and secure authentication workflows. These safeguards help reduce authentication failures and prevent unauthorized access attempts that may trigger a 401 error.
• Keep your systems regularly updated: Regularly update your CMS, plugins, authentication tools, and server software to maintain compatibility and security. Outdated software can introduce vulnerabilities or configuration issues that interfere with the authentication process.
• Ensure permissions and rules are accurately configured: Review authentication rules, access controls, and user permissions regularly to ensure legitimate users can access protected resources. Incorrect access settings may unintentionally trigger 401 errors by blocking valid requests.
• Educate users on securing login information: Encourage users to protect their login information, use strong passwords, and avoid sharing account credentials. Incorrect, compromised, or outdated login details are a common cause of authentication-related issues.
• Conduct regular testing: Test login flows, protected pages, and authentication systems whenever you make changes to your website, plugins, or server configuration. Regular testing can help identify potential issues before they affect users.
• Use website monitoring tools: Website monitoring tools can track authentication activity, access failures, and recurring error responses across your website. They alert you to unusual login behavior and spikes in 401 errors, helping you identify issues early and troubleshoot them more efficiently.
• If using APIs, keep API authentication secure: Protect API keys, access tokens, and other authentication credentials, and update them when required. Properly configured API authentication helps prevent authentication failures that may result in 401 errors.
• Review login credentials regularly: Periodically review service accounts, shared accounts, stored credentials, and authentication tokens to ensure they remain valid and up to date. Expired or incorrectly configured credentials can prevent successful authentication.
• Monitor plugin and security tool changes: Security plugins, firewalls, and authentication-related tools can introduce new access restrictions after updates or configuration changes. Review authentication functionality whenever these tools are added, updated, or reconfigured to avoid unexpected access issues.
• Review session and access settings: Check session timeout policies, authentication requirements, and access-control settings regularly to ensure legitimate users are not unintentionally blocked. After making configuration changes, test login sessions and protected resources to verify that access works as expected.
  

Frequently Asked Questions

Stay One Step Ahead of 401 Errors

Once you understand what causes a 401 error and how authentication works, resolving the issue becomes more straightforward. Whether the problem stems from invalid credentials, an expired session, browser-related conflicts, or a configuration issue, a systematic troubleshooting approach can help you restore access more quickly.

Taking proactive steps such as maintaining secure authentication practices, reviewing access settings, and regularly monitoring your website can help minimize future disruptions. The better you understand authentication-related issues, the better equipped you’ll be to keep your website and online services running smoothly.

If you’re looking for a reliable foundation for your online presence, BigRock’s web hosting and website solutions can help simplify website management while giving you the tools needed to maintain a secure and accessible website.