After you change the Task content type for a SharePoint site collection, you cannot synchronize task items on a newly created Task list
Symptoms
After you change the Task content type for a SharePoint site collection, you cannot synchronize task items on a newly created Task list. When you try to save the changes, you may receive the following error message:
Send/Receive error – Click here Even after you revert to the previous Task content type, synchronization still does not work.
Resolution
To resolve this issue, apply the following hotfix package:
968857?(http://support.microsoft.com/kb/968857/) Description of the Windows SharePoint Services 3.0 hotfix package (Sts.msp): April 28, 2009 Limitation After you apply the hotfix package, you cannot resolve the issue for the existing site collections. However, this issue will not occur for the new site collections.