This has happened twice in the last year, most recently the other day. I was online and all of a sudden my connection dropped, and a UAC pop up (on Vista SP2) says that Windows needs to install drivers or something or other for the modem (ZTE MF 668). I just clicked cancel, unplugged the modem, put it back in and connected again.
As far as I know everything's installed correctly - it must be otherwise surely it wouldn't work in the first place. Anyone else experienced this?