If you are getting 500 internal server error in CentOS Web Panel (CWP), this tutorial will help you.
Generally, the error occur because of the permissions issue.
suPHP requires that the files are owned by the user name, and suExec requires that they are executed from the correct home folder.
Permissions on php files should also be set to 644 (-rw-r-r-), folder permission must be 755.
Change ownership on the files and directory
Login into the admin panel
Left Menu –> User Accounts — > Fix Permissions and select user.