I have used the Kenwood software and also Link 700 to program the D700A.
What cable are you using? Using a Radio Shack RS-232-C cable, this has all pins but 1 & 9 connected straight through, 1 & 9 are not used, see page 2 of the Specialized Communications manual. Check the properties of your com port on the computer, under advanced place a check mark by "Use FIFO buffers".
Also check this web page: RV3APM: about TM-D700 http://www.qsl.net/rv3apm/TM-D700.html