I'm having quite the same problems as Gary on this list when doing a /etc/init.d/isdnutils restart.
My brandnew Potato installation remarks: Starting isdn services : interfacesippp0: Invalid argument ipppd iprofdSorry - isdnPPP driver version 0.0.0 is out of date. Maybe ippp0 has no 'syncppp' encapsulation? Could this be due to a fault in the files device.ippp0 or ipppd.ippp0? /var/log/messages reports: ippp0: syncPPP not configured. Does the isdn system need syncronus PPP to build up a ISDN connection? (I'm located in Germany) The card seems to be perfectly recognised as /var/log/messages contains no error after bootup. Any help is grately appreciated Robert