Danny,
I finally found out what the problem was. The adapter cable is good, however, the software was looking to another USB device (memory card reader) and not looking at the COM7 port. After being on the phone with Garmin Tech support for over an hour - and not getting anywhere; I decided to start unpluging items. The only one I unplugged was the card reader and the problem was solved. I have down loaded several caches with no problems. Pass it on.
Bill (aka 2BionicKnees)