Set Database Multi User

use master
GO

select
    d.name,
    d.dbid,
    spid,
    login_time,
    nt_domain,
    nt_username,
    loginame
from sysprocesses p
    inner join sysdatabases d
        on p.dbid = d.dbid
where d.name = 'dbname'
GO

--=> kill the number in spid field
kill 56
GO

exec sp_dboption 'dbname', 'single user', 'FALSE'
GO