Called in to make a minor modification, making one extension ring immediately on six CO lines, matching that of the port 1 (OPE) extension, I cannot enter program codes manually. After logging into the program mode, I can browse the first dozen codes (001 through 013) but, when I attempt to enter 603 (or any three-digit code) it responds with three-beep error at the third digit. Everything else on the system, programmatically and operationally, is fine, but I can't do anything beyond the first dozen programming options. We did not install this system. Is there some manner that programming at the OPE phoneset (7436) has been disabled?