Since recently, I started to have difficulties restoring a backup of the database. I always had this database is in used. The only way I have found to be able to restore is to add a Single User approach :

USE Master
GO

ALTER DATABASE DatabaseName
SET SINGLE_USER
WITH ROLLBACK IMMEDIATE
GO

RESTORE DATABASE DatabaseName FROM DISK = N'D:\Data\DatabasePath\DatabaseName.bak'

Anyone would know why I have to do this now?