We haven’t seen this error ourselves, but it may be out there lurking in wait for one of our unsuspecting clients (or yours): http://blogs.technet.com/b/msonline/archive/2010/07/08/outlook-2007-patch-required-to-prevent-sharepoint-list-item-duplication.aspx
Loryan Strant, Microsoft 365 MVP
Consultant, writer and speaker