I was composing a response email to explain that I'd tried it more than 20 times to no avail. Before hitting send I decided to try it again. Finally I got the data to upload to the radio; however, I can't discern anything I did differently on the final attempt.
Ah, okay. As far as I could tell, I get once chance to start the transfer with the radio. If it fails, the radio has to be rebooted into clone mode before it will try again. Does anyone know if other programming software is like this?
As far as what's different, I think the procedure needs to be:
1. Connect the cable to your serial port and to the radio 2. Power on the radio into clone mode 3. Get chirp to the clone settings dialog 4. Hit the button on the radio that puts it into receive mode 5. Click okay on the chirp window
If there's a required delay between 4 and 5, I can enforce that in the code. While I had the radio I was able to get the procedure down fairly repeatably, but it is definitely the most fragile cloning process I've seen.