Sorry about PM, was just reacting as I just got home (not that it's been much longer now).
Hmmm, is Vista updated? That could cause issues (there new stuff out, I got hit this morning with a bunch of patches and I running Home Premium).
Have you tried the stick in another USB port (sometimes things do wear out so there isn't the proper connection, try another USB port)?
Does/did the stick work ok now/in the past with XP (if it does/did, it SHOULDN'T be a hardware issue but I seen things die just because you dared to unplug them).
I really struggling without seeing error messages, what does it say about the stick when you look at it in the "device manager" (my Vista is in Dutch so it has a different name)? Might be a clue there.
Once we rule out the "obvious" then we only have the impossible to deal with, and with Microcrap software the "impossible" is usually easy