I have the same problem. I bought an eXplorist 500 LE and loaded the Geocache Manager on my Vista machine. I wasn't able to transfer GEOcache points to my receiver. I received an error message saying "No unit detected". I called the 1-800 tech support line and was told they're still working on the Vista update for the Geocache software and that, if I had an XP machine, it would work. UNSAT answer but, fortunately, I do have an XP machine and was able to transfer my Geopoints using that.
Hopefully, I'll be notified when the Vista update is ready.