When I enabled web based OAB distribution, Clients aren’t downloading the Offline Address Book at all. In fact Outlook OAB sync was hanging in half way for long time. In Outlook, Sync Issues folder has this error message logged.
9:07:52 Error synchronizing folder
9:07:52 Network problems are preventing connection to Microsoft Exchange.
9:07:52 Microsoft Exchange Information Store
9:07:52 For more information on this failure, click the URL below:
13:37:40 Microsoft Exchange offline address book
When I tried to access OAB URL (http://mail.company.com/oab), I get site not found (500) error. I supposed to get an authentication box and OAB.XML file. So the OAB site folder lost permissions to the users.
I checked web.config file at C:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\OAB and saw no one has permissions (except local admins).
So the SOLUTION is give Authenticated Users to the C:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\OAB folder and contents to READ permission. That’s it. Problem solved.