restore db from .bak file that contains multi backup
try the following:

USE [MASTER]
GO
ALTER DATABASE [spetztest] SET SINGLE_USER WITH ROLLBACK IMMEDIATE
GO
RESTORE DATABASE [spetztest] FROM  DISK = N'c:\sdk.bak' WITH FILE = 74,  REPLACE,  STATS = 1
GO


Make sure that your session that you are using to do the restore is not using the database you want to restore.