The Internal Server Error is commonly caused by incorrect permissions of some files/directories on your account. We do not allow higher than 755 permissions due to the fact that our Apache web server runs PHP in SuExec mode. Please click here to find more information about the most common reason for the ISE500 error.

If you need to change the permissions of your files or folders you can do this from cPanel -> File Manager. After selecting the file or folder you can change the permission from the menu on the top menu. You can check exactly which files/folders have incorrect permissions in cPanel->Error Log.

For more information about this issue, please refer to:

http://kb.siteground.com/article/internal_server_error_500.html