I have an Outlook VSTO C# Addin for both OL 2003 and 2007. I am having a problem on 1 user's machine where Outlook hangs each morning (only first thing in the morning) after the user starts her machine. Outlook is in cache mode and starts the process of updating the cache (Updating folders ... in the status bar). Sometimes before and during the update status bar is shown, Outlook becomes unresponsive. It never crashes, but never returns control back to the UI. I was initially thinking this was due to my addin using background threads to update some configuration information. However, after modifying my architecture substantially, I've removed any interaction with the Outlook object model on the background threads. I have a number of systems with similar (though sometimes different fixes installed) and not problems. I'm running out of ideas to address this. Has any one seen a particular addin issue or particular update that would cause this issue?