Download and install the latest Service Pack which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.
1. Access the Assignments data list on the Prospect and Plans tab
2. Edit the Prospect whose manager has already been end dated
3. The edit form appears with no Prospect Manager listed here
4. Enter the same end date that you used before
5. Save this and the entry on the assignment data list disappears.