http://www.brentozar.com/archive/2011/08/dedicated-admin-connection-why-want-when-need-how-tell-whos-using/

http://msdn.microsoft.com/en-us/library/ms178068%28v=sql.105%29.aspx

To use in SSMS please follow up those steps.

1. Enable SQL Server Browser.

Many of case for Network-Related error message is due to this reason.

2. Please use “Database Engine Query“, File>New> Database Engine query

This is keyword.

Do not open using object explorer since DAC does NOT support multiple sessions.

3. Add “ADMIN:” in front of server name

ADMIN:localhost