If you are using the CS1K and it is not SIP, then it is AML.
What version of CCT are you running?
Okay, here are some things to check given the situation:
In the CS1K compare a TN that works with one that doesn't paying close attention to AST on the phones (TN) and IAPG set same as a working phone.
In CCT ensure your Terminal is entered with the word "Line " in front of it. It should look like those that are working.
Ensure you have the Terminal associated with the right Addresses (DN's).
Ensure you have the right workstation associated too.
Ensure the reference client is set for that workstation and you are using a user that is associated to that Terminal.
Good luck.