Ok - so I tried connecting my radio and cable to another computer and the difference in speed was just enough to matter and I was able to connect, pull down the current program (even though it was corrupted) create a new program with just one channel and changed the startup text to TEST and write to the radio.
Then I moved the radio back over to my computer, turned the programming speed down from High to Normal (I hadn't even noticed the setting previously) and was then able to successfully push the program up to the radio and all's good now.
If you run into a problem, you might want to try a different PC. Apparently the slight variations in USB speeds and Bus Controller types has an impact on the programming process. You might also want to check the communications speed and slow it down if possible for your model radio and software.
Cheers,
Gadget