Actually, this post was helpful:
I assume the shared calendar registry setting just means that the SharingAddin is registered. In Outlook 2007, what happens if you do:
Tools->Trust Center->Addins Then go to the bottom where is says Manage:
COM Addins should be selected. Hit Go...
Does the Zimbra Sharing Addin show up checked?
What about when you select Exchange Client Extension. Does Zimbra Client Extension show up checked
When I look at this, Zimbra Sharing Addin is NOT checked. When I check it, Outlook puts in the Load Behavior field "Not loaded. Certificate of signed and load at startup COM Add-in is not in trusted source List." When I restart Outlook, no error dialog appears. But when I look again at the Trust Center, the add-in is again not checked, and the Assertion behavior is still present.
This error "message" might be key, as I am guessing this important add-in is not loading for me. Not clear why. A Google search on this message brings up similar problems for other Add-in developers (Plaxo and Newsgator), with as of yet unknown explanations.
Problem with New install Vista Ultimate+ Office 2007 Ultimate Upgrade to version 2.6.7 of Inbox not working with Outlook 2007 Windows Add-In continues to be disabled by Outlook 2007 - Plaxo Forums Ryan's Look at Outlook Programmability : New articles and more
There are work-arounds proposed on these sites re: macro security... I can try them and report back here.
Could there be something set by my Administrators in the Security Policy that requires a particular kind of signed certificate in place to get this add-in loaded?
This Assertion drives me nuts, as if I hit enter too quickly after any e-mail I send, the Assertion dialog brings down Outlook completely, requiring a painful restart and recheck of PST files. I am really interested in helping you hunt down the cause of this problem.
-- Atul