If your Windows NT 4.0 clients, who connect via RAS, are unable to access the network, even with PING, you may have a firmware problem with your server's 3Comm/USR Courier V.Everything.
If the modem is configured to also receive incoming faxes, the firmware may not allow it to work in this configuration.
Contact 3Com/USR for fix.
To workaround this issue, you can dedicate a modem for both incoming and outgoing faxes, and a different modem for RAS.
If you can't dedicate a modem, you must update the fax strings in the Unimodem.inf file, to work with your firmware
revision, and then uninstall the modem and reinstall it with the updated Unimodem.inf file.