There is bug in Express Sync versions 1.00-1.04 that will cause syncing to fail. The error message in the HotSync log is:

The system cannot find the file specified.
Express Sync synchronization failed

The error occurs if the configuration dialog is never opened. The workaround is to simply open the configuration dialog box (see TN0006 for instructions), and close it by pressing OK. The cause of this error is missing registry settings. The act of opening and closing the configuration dialog will write the necessary data in the registry.

This bug has been fixed in version 1.05.