If you’ve accidentally changed the permissions (CHMOD) to some of your folders / PHP files and are now receiving a “500 Internal Server Error” you can fix this by changing the permissions to the default.

Folders: 755
PHP Files: 644

Note:
All folders / PHP files for your website should have the above permissions. Even if the script says you must CHMOD them to something else disregard it: we run a setup utilizing suPHP which makes it so your PHP processes are ran as your user, effectively eliminating the need for insecure permissions.