is this happening for everyone or only specific users? Any chance these users may have been moved from one Exchange server to another recently?
What version of Unity are you running here (including build)?
This could be related to a mailbox ID not being updated in our cache when a mailbox is moved (assuming that's the case) or an Exchange server (or servers) in the site were off line for a period of time (the IDs roll on you). Unity requests a handle to the mailbox using the cahced ID to speed things up (asking the directory where a mailbox is expensive and slow). If the handle returns not found we SHOULD then turn around and do the slow-query to the directory to see what the new ID/location of the mailbox is. We don't do this accurately in all cases and sometimes it's necessary to restart the Unity server to have to rebuild these ID lists from scratch, which we only do at startup. This is different than a normal cache sync which happens every 10 minutes or can be kicked off manually in DOHPropTest. The Mailbox Handle IDs are seperate from that and you can't force it to rebuild manually without a restart.
If you haven't had any Exchange servers off line/out of communication with Unity and you haven't moved any of these affected users, this probably isn't your issue. If you can't restart Unity for some reason and you want to drill down further, we can turn on some DOH/DAL traces and see what comes up in the diagnostics that might give us a clue as to what's going on.
Jeff Lindborg
Unity Product Architect/Answer Monkey
Cisco Systems
lindborg@cisco.com
http://www.AnswerMonkey.net (new page for Unity support tools and scripts)
