User unable to access OWA – HTTP Error 403.14

when a user tries to access OWA by entering the URL, it gets the following error:
HTTP Error 403.14 – Forbidden
The Web Server is configured not to list the contents of this directory.

However, I am able to access the OWA logon page when I login as administrator.

Could it be the the permission issues? How can i resolve this…

Thanks!