Cannot set a credential for principal 'sa'.

It was a little frustrating to get an error for a seemingly simple task but then agian maybe I screwed something up.  After doing a couple of searches i found a Microsoft KB (support.microsoft.com/kb/956177) "You receive an exception in SQL Server 2008 when you try to modify the properties of the SQL Server Administrator account by using SQL Server Management Studio".  It was for SQL 2008 but it worked for my SQL 2005 sp3 server just fine.  You have to click the Map to Credential check box but you don't have to add any credetials just click the OK button to complete and that's it.