I had duplicates in my calendar and followed the instructions...
No matter what I did, I couldn't get rid of one set of calendar items. When I synced, I got dupes back.
Here's how I fixed it.
Advanced > Select calendar > Clear > Backup > Save to disk > Open in text editor to make sure it's empty > Restore
I also took the battery out for a minute.
I'm not sure which of the above did the trick, but now my calendar is empty and I'm ready to sync again.