The OTA fixed all my sync-issues as well, allthough I managed to fix some of my calendar sync problems even before the OTA upgrade..
Have you tried the "category trick" as described in
this post?
If that doesn't help, try doing this:
1. In Outlook (on your PC), export your calendar to a backup file (just in case)
2. Empty your "Deleted Items"-folder in Outlook.
2. Still in Outlook, open your calendar and switch to list view (View -> Current View -> All Appointments)
3. Select all appointments and delete! (they'll end up in the deleted items-folder)
4. Now sync your phone.. Calendar sync should work without any errors basically because there are no appointments to sync!
(4. If it doesn't and you still have calendar items on your phone; delete these manually from the phone.. Might be a good idea to "clear data" in Settings - Applications - All Applications - Calendar storage)
5. Back in outlook, restore your appointments bit by bit.. Start off by restoring the first item starting with the letter A. Sync your phone. Hopefully the phone will sync just fine.. If it does, continue with even more appointments, eg. all appointments starting with the letters A-C or so... Sync your phone again.. If you're still all good, then continue this process untill all items are restored..
Now the clue to this process is to identify if there are any faulty calendar items that makes the exchange sync to stop.. In my case, using this "elimination method", I found that one of my appointments with "endless" recurrency caused the syncing to fail.. All I had to do was to delete that item, and create a new one..
Hopefully this will fix your problems.. Give it a shot and let me know how things worked out!