I'm not sure what the cause of the problem could be, is changing the response to key 8 a viable solution for you? The only other thing I can suggest is to try updating your modem drivers, it could be some problem with the driver correctly detecting and relaying the key presses to IVM. I haven't used IVM with TAPI modems in a while, so I can't remember if IVM actually has built-in audio signal processing to detect DTMF itself, if so the problem could exist within IVM and perhaps it is over-sensitive and pick-ing up the key 8 even when it is not pressed.