Server running Ubuntu 8.0.8 LTS 64 bits, zimbra NE 6.0.7
Client running windows 7 64 bits, office 2007 with SP2, connector 6.0.5981
Reproducing the problem is "easy": Close outlook while the send/receive task is processing, and next time you will start outlook, it will crash. If you wait 5 to ten minutes, Outlook starts normally.
I tried upgrading the ZCO to the last version (from the admin/downloads page) but to no avail.