When I try to sync my iPad, I get an "Unknown Error (-39)" It still seems to sync most things - the error occurs late in the sync toward the end of the last step, which seems to be photo-related, and my apps are up to date, etc.

The main thing I've noticed that's off is my pictures - when I open the pictures app, I get a message saying: 


  iTunes Sync Needed - High Resolution
  images synced via itunes are missing. 
  Connect your device to the computer
  you sync photos from and launch iTunes
  to sync them.


Since the issue seems like it might be photo-related, I tried repairing my Aperture library's permissions and database - no help.

Any ideas?
Try turning off photo sync completely, syncing, and then turning it back on.