The best way is to rebuild your client profiles. This is of course a total pain in the arse but there you go.
Heres the steps I take (I use win xp pro sp3 + outlook 2007):
1. go to control panel/mail
2. delete any mail profiles you have there.
3. go to control panel/add remove programs
4. remove zimbra outlook connector
5. restart pc
6. gather settings for client profile ie mail server/user/pass
7. install zimbra outlook connector
8. start outook
9. enter server details
10. let Zimbra resync -- this is an overnight process for me
