System not detecting live caller

I have a few instances of vicidial running. On one of my instances it no longer detects that the phone has been answered. Can someone tell me why it's not detecting the person answering the other end of the line?
VICIDIAL astGUIclient discussion forum
http://forum.eflo.net/VICIDIALforum/
http://forum.eflo.net/VICIDIALforum/viewtopic.php?f=4&t=5991