Good suggestions...

I define the machine names within a config file, in an array of hashes. I'm calling $Registry->Connect from within a subroutine, which is called from a loop that pulls the names out of the array. I went back and doubled checked the machine names, and they are correct. I also just double checked that the registry key name didn't change between XPSP2 and Vista, and the key names are the same.

Fortunately, neither was the issue, and I don't feel too dumb, yet. :) However, that eliminates a really easy fix.