VSTO for Outlook just died. Ressurect please.

Well, just died is actually a bit inaccurate. My Visual Studio Tools for Office Outlook solution stopped working friday, just about 10 minutes before I was supposed to hand it over to the customer.

When starting the project in debug mode nothing happened. The addin was displayed int the COM Add-Ins section in Outlook, but was unchecked. When I tried to check the addin Outllook simply unchecked it for me again. This of course lead me through the entire VSTO architecture trying to figure out what was wrong. The CAS settings was scrutinized, and I created several new test projects to try to get my debugging back on track.

Realizing that there is very little content on VSTO out there and that VSTO is simply a thin wrapper for old-school Outlook development I turned to the vast knowledge of COM addin developers. My hero of the day is Josh Einstein who explains how Outlook quarantines COM Add-Ins if they don't behave. For VSTO apps all managed plugins are loaded through the VSTO loader, so if something goes horribly wrong with one of your VSTO apps, none will run. What you need to do is to go in Help -> About in Outlook and open Disabled Items. Here you'll probably find the VSTOLoader.dll  (or was it VSTAddin.dll). Remove it from disabled items and you're good to go.