In /Library/Modem Scripts there are all the drivers for most every modem. Maybe it became corrupted, or its permissions got weird. The latter should be Owner = System (Read & Write) Group = admin (Read & Write) Others (Read Only) and the file is locked, closed padlock. Repairing them might help. You could always send him your folder if his is corrupt, as long as you have equivalent systems, and he makes sure to adjust the permissions as above.
Hope this is of use.