If your unplugging and plugging the stick alot,that will cause a problem sometimes too.
Be sure to use the same port everytime,if you plan on using a powered hub,same thing goes,use the same port to plug the hub into. Otherwise your apt to have the same problem that Imadot spoke of.

PS: check the sticky for tips/tricks to make vista work better,UAC can be turned off and you can set your login to admin.
FWIW: I use admin to start AH always,seems to work better in Vista that way.