When you do a restore, you need to kick everyone out of that database, or else they will hold a lock on that database. What I do, is set the database to RESTRICTED_USER, before a restore, just to make sure that no non-admin user can get in. You can also set the database OFFLINE, if you have some applications that for reasons beyond your control are running as administrators. Remember to use the WITH ROLLBACK IMMEDIATE option, as well. Otherwise, you have to wait for the users to politely finish up.