Sync issue with PDA

Running Vista Home Premium i have created a partnership with a Dell Axim -
easy enough.
My issue is that on each sync connection, both Outlook 2003 and the PDA end
up with multiple entries of the same calendar entry - on both devices.
deleting the multiple entries and resyncing simply puts the multiple entries
back into the calendar.

Other parts of Outlook are unaffected.

In XP if this happened, I could insstruct Activesync to ignore duplicates -
but cannot seem to find that option on Sync Centre.
Any ideas anybody??

Thanks.