The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact your web hosting provider and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
This error occurs for several reasons. You may find the reason in cPanel, menu "Error Log". There you can see the last 300 errors.
Possible reasons are:
1. Wrong permissions on file and/or folder – the maximum rights that are allowed are 755
2. Invalid lines in the .htaccess file
3. Your PHP script uses lots of memory and reaches the limit of memory in php.ini