Could not connect because the maximum number of '1' dedicated administrator connections already exist.

Applies to: Microsoft SQL Server 2005.

Error Message.

Event Type: Error
Event Source: MSSQLSERVER
Event Category: (4)
Event ID: 17810
Date: 2/6/2008
Time: 5:32:02 PM
User: N/A
Computer: SERVSQL
Description:
Could not connect because the maximum number of '1' dedicated administrator connections already exists. Before a new connection can be made, the existing dedicated administrator connection must be dropped, either by logging off or ending the process. [CLIENT: 127.0.0.1]

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.
Data:
0000: 92 45 00 0
0008: 07 00 00 0
0010: 4f 00 50 0
0018: 00 00 00 0

Cause.

Only one DAC is allowed per instance of Microsoft SQL Server. When a DAC connection is already active, any new connection attempt through DAC will get the following error message on screen:

HResult 0x40, Level 16, State 1
TCP Provider: The specified network name is no longer available.
Sqlcmd: Error: Microsoft SQL Native Client : Communication link failure.

An error message is also logged on the Application log as shown in the first image of this page.
 

Solution.

As the error message states, drop the existing connection, before attempting a new connection, or use the existing connection. Only one connection is allowed.

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