I just fixed an OWA problem by resetting the exchange iis virtual directories as described in this article: http://www.msexchange.org/tutorials/Resetting-OWA-Folder-IIS-security-permissions-Exchange-2003.html
it seemed to work wonderfully but now my mobile users are having trouble accessing Active Sync. They have been using Active Sync on their windows mobile phones for awhile and now they are seeing the login prompt and are unable to log in. I think perhaps I need to change the security settings on the active sync virtual directory but I'm not sure what to choose. At this point there are no items checked in the Directory Security Authentication Methods dialog box for the Active Sync Virtual Directory.