Not sure what you mean by you've stopped SQL here - SQL doesn't show up in the task manager - you can stop the SQL services in the Service Control Manager and then restart them when you get this message which should "shake off" any clients which may have attached themselves (the SA can do this when you fire it up).
Presumably Unity is up and running, taking calls and all that good stuff - if so the DB should be up and running and available - if you get that error message open up the SCM (leave DiRT restore running where it is) and shut down the SQL services there then restart them then try to continue. If you continue to get that error message then something is not complete about your install and the SQLDMO connection is being denied for some reason.
