We're currently in the throes of transitioning to Exchange 2010 and are running with a 2003/2007/2010 coexistence. We haven't had any problems until yesterday when a number of users who have been moved to 2010 were unable to open Outlook and it comes back with an error saying: Either there are network problems or the MS Exchange Server Computer is down for maintenance. This can be with any client, 2003, 2007, 2010. Outlook Web App works just fine and occasionally a clean client with fresh profile will work.
I thought that it might be to do with the encrypted traffic, however this box is checked and they were able to open their mailbox via Outlook the day before. I tried turning off encryption to the CAS entirely and that didn't make a spot of difference. There aren't any DNS problems as far as I can see and given that OWA works pointing to the same server, that wouldn't make sense.
Having searched extensively, the only solutions I can find are when you can't access a mailbox from ANY Outlook client, rather than some working. Therefore these solutions haven't worked or just don't apply. I haven't been able to find anything where the problem isn't as clear cut.
Any help appreciated!