Hi Phil,
Thank you for using Microsoft My Phone. As I understand your situation, you were previously using the My Phone beta (version 1.1) but ever since the launch of My Phone 1.5 (which was on 10/6), you've not been able to successfully sync your data.
This might sound odd, but can you uninstall My Phone then reinstall the application from
http://myphone.microsoft.com/install? You can uninstall the application by going to Start Menu > Settings > System > Remove Programs.
If you're still unable to sync after reinstalling My Phone, you might want to try unselecting all the types of items that you're synchronizing and adding them back one at a time and sync'ing after each time you reselect one of those items. This will help determine if there is indeed something that is "corrupt" that you're trying to sync.
Hope this helps,
Richie Weldon