I'm going to try my best to help anyone out stuck in this situation because it took me ages to sort out! BUT please note that my scenario may not be the best or the easiest or even the most accurate!
So my scenario was I had Server 2003 standard with Exchange 2007 VLK enterprise, all clients with Outlook 2007 couldnt enable OOF (Out Of Office) they had to go into Outlook Web Access to enable it.
After some initial digging I found out that I had to look at the certificate in exchange incase it was invalid as well as check the autodiscover service to make sure it points to the right place.
1. Check your certificate!
2. Check in outlook the autodiscover settings
what URL's are pointing to where by holding control and then right clicking on the outlook icon in the system tray then select test autoconnection. This will show you the URL's it is using.
3. Internal / External URL Check
Check your URL's for Outlook within the Exchange Management Shell
"Get-WebServicesVirtualDirectory | fl InternalURL,ExternalURL" run this command and make sure that the URL's are correct. You should change them if not, then try again.
Does this help anyone...?