ALTER DATABASE failed because a lock could not be placed on database
USE master;
DECLARE @killSessions varchar(8000) = '';
SELECT @killSessions = @killSessions + 'kill ' + CONVERT(varchar(5), spid) + ';'
FROM master..sysprocesses
WHERE dbid = db_id('dbname')
EXEC(@killSessions);
ALTER DATABASE dbname SET SINGLE_USER WITH ROLLBACK IMMEDIATE;
GO
ALTER DATABASE dbname SET OFFLINE WITH ROLLBACK IMMEDIATE
GO
ALTER DATABASE dbname SET MULTI_USER;