If you get an error: Synchronization failed with non-Outlook items (and if Outlook items like contacts sync fine) in Activesync 4.1 with a Windows Mobile 5.0 device, then are two things you might want to try out:

1) Delete Activesync partnership from desktop and device and then recreate the partnership
2) If Step 1 does not work, the only other option is to Hard Reset the Pocket PC and reset it to factory defaults

For Activesync/ Windows Mobile paid support options, click here