Windows NT

Support Menu

Last Updated On: 08/05/2004

Troubleshooting Devices

RAS and Modems

Problem: Modem installation:
Solution: Do not skip COM ports when installing a modem. Use the next sequential port for installation.

Problem: Error 692: Hardware failure in port or attached device:
Solution: Windows NT generates this error when it does not receive an expected response from the modem. Reset the modem by powering the modem off and back on. External modems usually have a power button for cycling power. However, internal modems reset only after completely power down the computer. On some newer machines with advanced power management, it may be necessary to unplug the computer to completely reset the modem.
Solution: If the computer contains a 33.6K or 56K modem (purchased after January 1996) update the mdm3comv.inf file from Http://


  • Error 629: The port was disconnected by the remote server
  • Error 733: The PPP control password for this network protocol is not available on the server
  • Error 734: The PPP link control protocol terminated:

Solution: These errors are frequently displayed when a user attempts to connect to a RAS using the incorrect protocol, or an incorrectly configured protocol. If this is the case, remove all protocols except for one, configure the protocol correctly, and retry the connection.

Problem: Error 633: The port is already in use or not configured for Remote Access dial out:
Solution: Most often, Windows NT displays this message due to a faulty Unimodem driver. This occurs after upgrading Windows NT 3.51 to Windows NT 4.0. The old Unimodem driver is retained, because it is in use by a non-Unimodem driver or service. To correct this issue, remove any non-Unimodem drivers, then install the Windows NT 4 Unimodem driver.

Problem: Cannot connect to an Internet Service Provider (ISP):
Solution: In the case that a user cannot connect to their ISP using RAS try the following:

  • Disable LCP extensions for older systems that do not support LCP extensions over PPP connections (open the Phonebook settings, Server tab, and remove the check from the Enable PPP LCP Extensions check box).
  • Disable IP header compression (found under Properties dialog box for TCP/IP under Network Properties).
  • Disable all dialup networking protocols other than the one required by the ISP.
  • Change the authentication type to plain-text and logon names in case the ISP does not support encrypted passwords.