500 Internal Server Error
This usually means the server has encountered an error and more information about the error can be found in the server logs.
Most of the time, that is a PHP error and it is recommended to enable PHP error_display in order to see what exact error is generated.
Also check general troubleshooting guide.
Note: You can enable PHP error_display from your hosting provider control panel, consult with your hosting provider for more information about how to do this.