Unspecified Error.
Applies to: Microsoft SQL Server 2005 SP3, Microsoft SQL Server 2008.
 
Problem Description.
 
When we open SQL Server 2005 Management Studio, get connected to a SQL Server 
2008 instance, and we try to modify the structure of a table making a right click on the 
table, and choosing Design, then we receive the following error:
Microsoft SQL Server Management Studio
Unspecified error
(MS Visual Database Tools)

Cause.
When you are connected to databases created on SQL Server 2008 instances using 
SQL Server Management Studio 2005, you cannot make use table design features 
against the tables of those databases.
Solution.
You need to use SQL Server 2008 Management Studio to perform table design 
changes on databases created on SQL Server 2008 instances. Table design 
functionalities of SQL Server 2005 Management Studio can be used only on 
databases created on SQL Server 2005 instances or previous versions of SQL 
Server.