Hi Robert,
Have you tried to look into the details menitoned in the error?
1. Check the agent properties in the configuration manager and see what device is assigned and also see if that device target (phone) is configured.
2. Check the media termination configuration. What it means is whether you are using hardware phone or a software phone?
3. Last thing you want to do is to check the call manager and specifially see and make sure that the device used to login is associated to the CCM JTAPI USER.
Nothing turns out, there should be a file called "agent.log" in the CAD machine. Try to go through the log, it should give you some clue. Let me know what you find!
Cheers,
Rajesh