An extreme warning needs to be added to this. If you set the database to single user from SSMS, then only THAT session can do anything with the database. You can't even use the explorer window because that's a different session. But, that's NOT the worst of it. If you make the mistake of closing the session that set the DB to single user, you stand a huge chance of a Web Service other some other functionality grabbing that single connection and you won't be able to change it without killing EVERYTHING that touches the database. If you can't find all of that stuff, then it may require a reboot in the "maintenance" mode so that you can actually fix it.

So, here's the warning...

[font="Arial Black"]DO NOT CLOSE THE CURRENT SESSION IF IT IS THE SESSION THAT SET THE SINGLE USER MODE!!![/font]

😉