Got stumped today.What would cause 4 ground start lines which are testing ok at the demarc, but when they go into the subs NEC PBX the lines are "picked up" but when you try to enter an extension,you hear the buttons beep but you aren't directed anywhere.You are defaulted to the operator who then connects you through.This is happening only on 4 lines out of more ground start lines going into the PBX.The NEC tech changed some cards but to no avail.Could DTMF be an issue?If so how is it tested?How or who can see it and adjust it?The switch is a DMS100.Any help is greatly appreciated.