since running Zimbra Desktop and Zimbra iSync Connector on my Mac, always get the Message: "Sync cancelled".

I'm running MacOS Snow Leopard (10.6.5) with iSync Connector version 6.0.2495 which seems to be the latest.

Settings are set to every day synchronization including all contacts and iCal CalDAV sync. Advanced settings: "Show data change alert" enabled.

As described: no sync, neither in iCal nor the MacOS adress book.
Have tried to delete sync history in the isync application, no success. No proxy is set.

Does anyone have an idea?
Thx in advance.