It was not an overwritten usb-drive, but MinGW complaining about a missing drive, that was present when builing MinGW.
I am not sure, if this was the case for the MinGW version provided with 10.05.
And we all (windows users) know, that the windows usb-drive management is poor (or at least was poor on xp and most likely vista), so it was a wild guess of mine, that there went something wrong with it.
And if it is really the case and not just a "funny" coincidence, it is either windows or the usb-board (and its drivers) which is to blame in my opinion.