I'm connecting to SQL Server (2016 and 2017 latest builds) via the Dedicated Administrator Connection (DAC) from PowerShell.

The following error message is recorded in the SQL Server Error Log:

> Date      4/2/2019 1:59:13 PM
> Log       SQL Server (Current - 4/2/2019 1:59:00 PM)
>
> Source        Logon
>
> Message  
> 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]

The query runs successfully.  Numerous connection string management iterations have been attempted; this one is the most robust so far.  

A solution exists on Stack Exchange that involves killing the spid before closing the connection, but that also throws a nuisance message into the SQL Server Error Log, so no joy there.

Examining `sys.dm_exec_sessions` reveals nothing of interest; no connections remain open using this technique.  The below PowerShell has a dummy query in it, I can't talk about why we are connecting this way because it is proprietary, but it is 100% necessary, it is a very quick connection, and I need to do it once every 10 minutes. 

This error is just noise.  The DAC query runs and works as expected.

The error is recorded *every time* even with a fresh restart on a quiesced system.  There are NO other DAC connections in use - if there was, Powershell would throw an obvious error message at the command prompt.

Interestingly, when using `sqlcmd`, no error message is recorded in the SQL Server Error Log. 

    #begin powershell script
    $SqlServerName = "server\instance"
    
    $DbQuery = "
    INSERT INTO  master.dbo.sometable(value1,value2) values ('test14','testtest14');"
    
    function Get-SqlConnection
    {
        param (
            [String] $SqlServerName
        )
        $sqlConnection = $null
    
        try
        {
            $sqlConnection = New-Object System.Data.SqlClient.SqlConnection
            $sqlConnection.ConnectionString = "data source=admin:$SqlServerName;Integrated Security=True; pooling=false"
            $sqlConnection.Open()
        }
        catch
        {
            if ($sqlConnection)
            {
                [void] $sqlConnection.Dispose()
            }
            throw
        }
        $sqlConnection
    }
    
    try
    {
        $sqlCommand = New-Object System.Data.SqlClient.SqlCommand
        $sqlConnection = Get-SqlConnection -SqlServerName $SqlServerName
        $sqlCommand.Connection = $SqlConnection
        $sqlCommand.CommandText = $dbQuery
        [void] $sqlCommand.ExecuteNonQuery()
    }
    finally
    {
        if ($sqlCommand)
        {
            [void] $sqlCommand.Dispose()
        }
    
        if ($sqlConnection)
        {
            [void] $sqlConnection.Dispose()
        }
    }

No connections are shown when I run this query on the server:

```
SELECT
    CASE
        WHEN ses.session_id= @@SPID THEN 'It''s me! '
        ELSE '' 
    END 
    + coalesce(ses.login_name,'???') as WhosGotTheDAC,
    ses.session_id,
    ses.login_time,
    ses.status,
    ses.original_login_name
from sys.endpoints as en
join sys.dm_exec_sessions ses on
    en.endpoint_id=ses.endpoint_id
where en.name='Dedicated Admin Connection';
```