Unfortunately the links in the Google hits seem to be out of date (well the
few I tried). However the problem has been resolved. First I got it with
emails as well, but then cleared out deleted items and it was OK. Must have
exceded some limit on number or size of deleted items.

"Brian Tillman [MVP - Outlook]" wrote:

"Ray Warburton" Ray wrote in message
...

When I try and delete a contact I get "The messaging interface has returned
an unknown error." I've tried restarting, rebooting and the repair facility.
Any suggestions please?

Google is your friend.
http://groups.google.com/groups/search?q=group%3Amicrosoft.public.outlook.*+messag ing+interface+has+returned
--
Brian Tillman [MVP-Outlook]