I chose the fax number from speed dial and also entered it manually. I have sent faxes to this number before. The machine has a touch screen. When I hit send the screen tells me the fax is being sent to the number I selected. Suddenly the number on the screen changes the moment the documents start to send to my home/fax number and the machine in our other office answers and the fax is received. I can't figure this out. I have tried faxing to other numbers and the same thing happens. If I go into the other office and use that fax machine I get a faulty line code. If I unplug the phone line from the new machine I am able to send faxes from the old machine. Weird. Sometimes I hate technology.

What happens if you unplug the old fax machine?

Are you using the phone cable that came with the unit? The 8500a uses a 2 wire phone cable. If you use a 4 wire cable to the phone jacket it could be causing unpredictable results.