[sza3434]

Most of the time when this happens (and what works for me) is to delete the mobile device from active sync then reestablish the connection.

Remove your phone from USB.
Pull up Active Sync
Go to File>>Delete Mobile Device
DO NOT DELETE YOUR MOBILE DEVICE FOLDER OR ALL YOUR INFO WILL BE LOST
Just delete the connection SAY NO TO DELETING YOUR FOLDER.
Reconnect USB to Phone
Reenter settings and you should sync