This error is due to not having connectivity to the machine and port of where the database is running.
All DevTest ports must be bi-directional including ones to the database.
To troubleshoot, do a telnet from the Workstation machine to the machine and port the database is running on and make sure you get a good connection.
You will also have to open Workstation port 2008 to accept communication from the database machine.
Once the firewall is open, this should resolve the issue.