"Cannot write the phone book file."

This is a Windows Nt 4.0 Error.

You could uninstall and reinstall Dial Up Networking.

Check in the system32/RAS directory for a file called "RASPHONE.PBK". If this file is there, rename it to something (ie rasphonepbk.bak) and run the "RASPHONE.EXE" which creates a new one. If there is no "RASPHONE.PBK" then run "RASPHONE.EXE" to create a "RASPHONE.PBK" entry.