Is this related to the SSL issue we have also been seeing? I think I understand that part of it now (no UC cert with the local domain name). But this keeps popping up on every user since we moved from Exchange 2007 to 2010.

How often does this pop up? Every time they launch Outlook? Or only occasionally? If they confirm this box (by clicking on OK), does Outlook start working correctly? Jim McBee - Blog - http://mostlyexchange.blogspot.com

Yes, it works once you click Ok. It always comes up when you start outlook and then randomly afterward. (I still have the Exchange 2007 server connected to the domain as a CAS even though we don't plan to keep it, so I wonder if it is picking up some autodiscover setting from there that is causing the prompt.)

So it is indeed the old server causing that prompt. I had shut it down for the night and when I turned it back on today the prompt came up the second it was online.

Hello, Thanks for sharing the solution with us. For more detailed information about autodiscover service, please see: http://technet.microsoft.com/en-us/library/bb124251.aspx Thanks, Simon