You can try reinstalling the Desktop Manager.
Or deleted the syncing partnership:
1. Close Desktop Manager
2. Open My Computer
3. Open Hard Drive (Local Disk C
4. Open Documents and Settings
5. Open the folder with your computer user name
6. Open folder Application Data
7. Open folder Research In Motion
8. Open folder Blackberry
9. Delete folder Intellisync
10. Reopen Desktop Manager
11. Setup your sync again and test.