Cannot delete this object because it is open in a designer.
The selected database object is currently open in a designer. If you want to delete this object, you must close the designer and then choose Delete on the shortcut menu.
See Also
Other Resources
How to: Delete a Database Diagram (Visual Database Tools)
How to: Delete Tables from a Database (Visual Database Tools)
How to: Delete a Stored Procedure (SQL Server Management Studio)
How to: Delete Views from Databases (Visual Database Tools)