Hi, My name is ***** ***** I am happy to assist!
Typically, older PBX systems aren't compatible with VOIP (Voice over IP) systems. Can you tell me if this is a newer PBX, or is this an older one? Do you also have the make and model of both the PBX and the phone?
Doing some digging on that issue -
Doublecheck the IP address, subnet mask address, PBX IP address, and default gateway address.
Barring that, there could be an issue with the IPCMPR or DSP cards, which means they will need replacement if that is the case.
Anything else I can do for you?