Check the extension is in the guest rooms form..
I would be checking the link. Is it over the network or a physical connection? Go to maintenance commands type PMS STATE. Is the link up or not? Do PMS TRACE ENABLE. Ask the hotel to make a test check in, do you see the name come across? Open a putty session telnet to the CCU on port 1752 and ask them to do a test check in again if it is on the network, do you see it there?
Possibly an issue with the check in system or link.
Regards