我需要重新启动数据库，因为某些进程无法正常工作。我的计划是使它脱机并再次回到联机状态。

我正在尝试在Sql Server Management Studio 2008中执行此操作：

use master;
go
alter database qcvalues
set single_user
with rollback immediate;
alter database qcvalues
set multi_user;
go

我收到这些错误：

Msg 5061, Level 16, State 1, Line 1
ALTER DATABASE failed because a lock could not be placed on database 'qcvalues'. Try again later.
Msg 5069, Level 16, State 1, Line 1
ALTER DATABASE statement failed.
Msg 5061, Level 16, State 1, Line 4
ALTER DATABASE failed because a lock could not be placed on database 'qcvalues'. Try again later.
Msg 5069, Level 16, State 1, Line 4
ALTER DATABASE statement failed.

我究竟做错了什么？