I am having a similar issue although I do not get a specific error message. After upgrading to v7.7 (with the latest v188.8.131.52 driver fix), I just see the "Exchange Mailboxes" group but no individual mailboxes. As a test, I un-installed v7.7 and re-installed v7.6 and I could see all the mailboxes again with no other settings changes. I was using the v7.7 client in both cases. I am guessing it is another bug. I'll have to follow-up with tech support unless there are any solutions already out there.
Has anyone had any success backing up Filestream enabled databases? I have been waiting for the 7.7 update and finally installed it but it seems to hang up after about 100MB of backing up my Filestream enabled DB. My other DB's seem to back up successfully. Additionally, when I stop the backup, the backup client hangs up and still says in use. I have to go to the client machine and restart the retrospect client. I have tried using a 3 authentication methods of connecting and all produce the same result. Any help is appreciated.