drive letter sudden change

[billyo]

i did a show last night and an hour before i started, i opened hoster, just to warmed up my gears, searched for a song and i was getting a no song in the database error, but to make a long story short, my ext. drive that used to be E:drive is now an F:drive, the drive is always been plugged in to the same usb port, i have never taken it out..i ended up rebuilding,and the night came out fine..i was just wondering what causes a sudden change..