I had the system pro installed with four phones and five lines hard wired. When my fifth new phone arrived, I plug it into the line the installer had left available, the phone LCD reads time and date, but when I remove the reciever, the tone is a busy signal and the LCD reads, "ERROR." I have the user manual for the system, but no programing manual. Is this a system problem, or does the new phone need to be programed, and if so, how do I go abopout it?