Well, this was a one-time problem that was solved by rebooting the Exchange server. At the time of the problem, I wouldn't have been able to move the original problem mailbox, because Exchange was unable to see the properties of it. Exbpa didn't show any problems. I was looking to see if anyone else has had a problem like this. Thanks.John

The problem started with only one person on the DB unable to connect (with Outlook Web App or Outlook) - eventually, nobody on that database could connect. Also, Exchange Management Console couldn't open Properties for the accounts on that database. There weren't any errors on the server related to the database, the CAS server was aware that the mailboxes were unresponsive, but the mailbox server didn't seem to know that the database wasn't working. I turned on ExMon while this was occurring, but didn't see anything different for these users. Thanks for the ideas.John

We are running Exchange 2010 w/ Update Rollup 5. Yesterday one of the mailbox databases became unresponsive, but EMC didn't show any problems; and there were no database related issues in the Event Log on the mailbox server, or on the CAS. The only anomalous error was EventID 9646 - specifically in regards to 'the maximum of 32 objects of type "session"' - I'd seen 9646 errors previously for users w/ too many folders, but it seems coincidental that these "session" errors would pop up only when there was a database problem. We tried to take the DB offline, but that procedure didn't work, so we restarted the mailbox server, and everything came back fine. Since the restart, there haven't been anymore 9646 "session" errors. Has anyone else seen this? My sense is that the DB problems weren't caused by the 9646 "session" errors, but that the "session" errors are caused by the DB troubles - unfortunately I didn't see any other errors, so I don't have any ideas for what to do to avoid this problem in the future. Any help would be appreciated. Thanks! John

Hi John, Any updates? Frank Wang

The problem started with only one person on the DB unable to connect (with Outlook Web App or Outlook) Hi John, Please move the mailbox to another database to test. You can also try to run the cmdlet New-MailboxRepairRequest against the mailbox. http://technet.microsoft.com/en-us/library/ff625226.aspx Please run the Exbpa to do a Health Check. Frank Wang

one of the mailbox databases became unresponsive, Hi Martin, What's the symptom when the mailbox database bacame unresponsive? Clients cannot connect to Exchange server? "If the third-party application or add-in typically opens too many objects on the server or leaves too many objects open on the server, other clients may be unable to log on to the server." A user mailbox has hit session limits http://technet.microsoft.com/en-us/library/ff360476(EXCHG.140).aspx "We tried to take the DB offline, but that procedure didn't work" What's the error message when you try to dismount the database? You can run the ExMon to monitor the connection and run the Exbpa to do Health Check. Frank Wang Forum Support Please remember to mark the replies as answers if they help and unmark them if they provide no help. If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com.