I wanted to update everyone on this topic which I wrote about a while
ago, as I have discovered the source of the problem.

http://groups.google.com/group/microsoft.public.outlook.program_addins/browse_thread/thread/9d51663980a36164/28a699d1cf6d8e82?hl=en&lnk=gst&q=outlookissueman+sql#28a699d1cf6d8e82

I posted a question about errors coming from Outlook when my add-in
was running. Users experienced problems in Outlook that did not
appear to be related to the add-in directly. For instance, if they
started a new email message and clicked the "To..." button, they'd get
the error "The messaging interface has returned an unknown error. If
the problem persists, restart Outlook.". When they tried to open a
recurring calendar appointment, they'd get the error "Can't open this
item. The operation failed".

We have since upgraded to VSTO and the Outlook 2003 and 2007 PIAs, but
that did not fix the problem. We recently saw mention of someone
having similar problems when using performance counters. Our add-in
code was logging some existing performance counters to our log file
every 20 minutes (e.g. % Processor Time, Available MBytes). When we
don't do that, the problem goes away!

Why accessing a performance counter from an Outlook add-in when SQL
Server is installed would cause Outlook to go a little crazy, I don't
know, but I'm glad we finally found it and wanted to pass the
information on to all of you.

Michael

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