Question : How do rows get into the msp_assignments_saved as opposed to the msp_assignments tables

We are trying to perform an UpdateStatus PSI (Project Server 2007) call in our home grown application and often get a message regarding with "AssignmentUidInvalid" even though we are retrieving the Assignment guid from Project Server.  We have noticed that when this does work there are matching rows in both the tables called msp_assignments_saved and msp_assignments, and when we get the actual error the value does not exist in the msp_assignments_saved table.  So, my qustion is, how are these tables managed and why is it that some rows are in both tables and sometimes the rows are missing from msp_assignments_saved?  How can I force the rows to be consistent in both the tables?

Thanks

Answer : How do rows get into the msp_assignments_saved as opposed to the msp_assignments tables

Thanks.  We are actually onto Project Support but it's like pulling teeth.  I had hoped there would be some folks out there who have seem this before.

Steve