Thank you, Flux56!
I was recently on holiday in New York and, right in the middle of a day of Geocaching, my eTrex Vista HCx suddenly became unable to get a lock. I thought the problem was the skyscrapers, but even with a clear view of the sky and a good long wait, it still refused to pick up any signal from the satellites. All it said was "Locating Satellites" or "Acquiring Satellites".
I was rather panicky that I'd bricked it. So we came back to the hotel (thankfully, free internet) and did some searching. After finding your post, I checked the firmware versions and, sure enough, I had the dreaded "version 0".
Now, I'd tried the WebUpdater on my previous Vista Cx and bricked that in the process but I figured I had nothing to lose this time. A few minutes later the HCx was fully updated and, joy of joys! it started locking onto satellites again.
My heartfelt thanks to you, Flux56. You're a life-saver.
For future reference, the web updater does not always work. Running the chipset software installer package will work every time.