Im near to 100% sure that the error "Internal Server Error" has nothing to do with cheveretto.
This script is a SIMPLE image share script...
Im sure it about perms and the suPHP.
I suggest you to not use root nor other user than the CWP user that you are uploading files for.
If you don't do that, you must fix perms, using as example the Menu->Users->Fix Permissions->user.
But if you upload the files using the user account you don't need to fix them.
Extra: Consider that suPHP is a new thing for non technical users, also for some PHP users that never heard about. It's a common mistake. Pin it to forum