An associate of mine used to have an ISDN line but, on moving house, has gone for BTBroadband. Knowing less about computers than your common earthworm he didn't seek help or follow instructions and now has a few problems. Initially the machnie failed to boot saying that the file 'NDISWAN.vxd' couldn't be found. We managed to get him round that one.
After some grief we got the BTBroadband (it's the business version- is there a difference?) installed and the modem installed.
When he tries to login in he is, apparently, getting an error - Error 645, Internal Authentication Error.