Steve Jones - SSC Editor (3/10/2016)
Are you using the DAC locally? Maybe show the connection string so we can be sure this is working?
In a cluster, you might need to log onto the node, not the virtual node. I'll try to find a reference.
I just tried using the DAC on a test cluster/AlwaysOn I have set up and it failed as well. I determined that I didn't have the port DAC was using open on my firewall. After I cleared that up, I'm able to use it locally on a node, or remotely, and it works with both the server names and the listener name.
Might make sure your firewall is letting that traffic through.
I found this info: "SQL Server listens for the DAC on TCP port 1434 if available or a TCP port dynamically assigned upon Database Engine startup. The error log contains the port number the DAC is listening on."