Hi, John -
I've seen a couple of references to this issue elsewhere. Some suggested fixes are below - if you've got time to try these, please let us know if any help you:
1. Ensure that Outlook is set as the default mail client under Tools > Options, as well as in Internet Explorer's Options section.
2. Verify that your firewall software (such as ZoneAlarm or OneCare) isn't blocking ActiveSync.
3. Check the Add/Remove programs panel on your PC and look for installed Outlook patches having to do with Junk Mail - some seem to attribute the error to these, and removing the patches supposedly fixes the issue.