Due to the use of suPHP on the VlexoFree server file permissions are restricted to more secure permissions.
For more detailed info see SuPHP#PHP_displays_500_Internal_Server_Error
The permissions of folders needs to be less then or equal to 755 (drwxr-xr-x).
The permissions of files needs to be less then or equal to 644 (-rw-r--r--)
Please note that suPHP does not allow permissions 666 and 777.
CGI scripts that go in your "cgi-bin" need to be 755.