There is bug in versions of Express Sync up to 1.02 that will generate the following error in the HotSync log:

COM error [-2147024809]: The parameter is incorrect.
Express Sync synchronization failed
  

This will occur if there exists a record on the handheld that when copied to the Windows Address Book would have no fields. Deleting this record from the handheld will correct the problem.

This bug is fixed in version 1.03 of Express Sync