Like many other Google Sync users on Blackberry, calendar sync stopped working some time between the end of November, 2008, and when I returned to network coverage areas in mid-January. No amount of uninstalling and reinstalling Google Sync had any effect. Luckily, I found a thread in Google Mobile Help that contained the solution. I'm on a Blackberry Bold 9000 on AT&T, v126.96.36.199 (Platform 188.8.131.52), and here are the steps I took to get Google Sync working again:
1. On a Windows machine, connect your Blackberry and run Blackberry Desktop Manager 2. Go to Backup/Restore, and then click on Advanced 3. In the device pane, select "Calendar" and "Calendar-all" (Control-click to select both) and click on Clear[^1] 4. On your Blackberry, uninstall Google Sync (requires restart) 5. Install Google Sync 6. Run Google Sync, enter your login credentials, and sign in 7. Go go Options, and de-select contact sync (I don't use it), and then select the Calendars you want to sync 8. Sync!
[^1]: Note that this will delete all calendar data on your Blackberry. You may want to backup.
I'm glad it's working again.