This bug I found in XP, Vista /all versions/
1. I dont have logical drive D: at my local hard drive. /only C:/
2. Map sth from another computer in local network as D:
3. Insert sth /i.e. flash/ in any USB slot of local machine
4. It doesn't work - USB device can't be open !!!
5. Disconect mapped D: and it works again

Why?? this happens only if you map sth as D: with any other letter no problem.
Try it please and say if I'm right or not.