Our comprehensive guide on web servers continues with an article on HTTP response codes.  Response status codes beginning with the digit "5" indicate cases in which the server is aware that it has encountered an error or is otherwise incapable of performing the request. Except when responding to a HEAD request, the server should include an entity containing an explanation of the error situation, and indicate whether it is a temporary or permanent condition. Likewise, user agents should display any included entity to the user. These response codes are applicable to any request method.

500 Internal Server Error, 501 Not Implemented, 502 Bad Gateway, 503 Service Unavailable, 504 Gateway Timeout, 505 HTTP Version Not Supported

Your Web server encountered an unexpected condition that prevented it from fulfilling the request by the client.

The best way to think of Internal Server Errors is as a catch-all error that can be dished out to a viewer for many, many reasons from port issues to just general server misconfiguration.

Of course you (as the webmaster) should check all of your files and scripts for errors, especially if you receive the error after an update or upgrade and perhaps consult any documentation for potential fixes to the problem.

To enable the display of errors for PHP, you should create a .htaccess (or edit your existing one) and add the following line to enable the display of errors:

php_value display_errors on

After doing so you should try to visit the page or site again and see if you're provided with any helpful error messages by the site, especially PHP error codes which can guide you to where the problem lies.

For the most part however 500 errors are not able to be resolved by the end-user and in many cases, even the webmaster cannot fix the issue so the best thing that can be done is contact support regarding the issue.