forum/ doesn't work, only with forum/index.php
 

Hey guys, have a problem with my forum.
I can't get to my forum via the usual url www.example.com/forum, I have to add www.example.com/forum/index.php which is really strange...

When visiting example.com/forum I get this 403 Forbidden message:
Forbidden

You don't have permission to access /forum/ on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

Can somebody please help me with this or try to direct me into some kind of direction?