FIX: Error message when you try to update the index key columns of a non-unique clustered index in SQL Server 2005: "Cannot insert duplicate key row in object 'ObjectName' with unique index 'IndexName'"
Source: Knowledge Base
Product: Microsoft SQL Server 2005 Enterprise Edition & SQL Server 2005 Standard Edition
Notification Contents: New and Major Modifications
FIX: Error message when you try to update the index key columns of a non-unique clustered index in SQL Server 2005: "Cannot insert duplicate key row in object 'ObjectName' with unique index 'IndexName'"
http://support.microsoft.com/kb/940937/en-US