There are a few things to do that could help:
1. Make sure you use a Null Modem Cable. As Scott mentioned this should have been with the 640/641. This cable should plug directly into your usb/ serial adapter but if you need to convert the gender, make sure whatever you use for an extension/ gender changer isn't also a Null Modem adapter. If it is, you will have a straight cable and it won't work like that. It would be best and you could rule out the cable if you only use the supplied cable.
2. In the program settings make sure you have the correct COM Port selected.
3. In the software go to "Network" then in that drop down "Address Tool", the software should discover your ZP.
I don't mind fielding a phone call either so if you need to give me a call 801 309 3055
Ryan