A listing in numeric order of Microsoft Dial-Up Networking (DUNS) Error codes with the Microsoft error message follows. If there's a hyperlink, you can follow it for more information on what to do about the error. If you are getting an error that does not have more information here, please let me know! The list includes error codes for Windows 95, 98, Me, NT, 2000, XP, and Vista.
In later versions of operating systems (NT, 2000, XP and Vista) some of the errors can occur for connections other than traditional dial-up modem connections: they may occur with DSL and VPN (virtual private networking) connections that do not involve dial-up.
NOTE: Some solutions indicate to re-install DUNs and/or TCP/IP. See this Microsoft KB article for Win 95/98 instructions to Remove & Re-install DUNS & TCP/IP. Newer versions of Windows don't allow DUNS uninstall: see Reset DUNS (TCP/IP) in Windows 2000 & XP.
Windows Vista: Dialing directly from the 'Connect To' menu or other shortcuts will not display DUNs error codes - instead, particularly large and unhelpful dialog boxes are shown as detailed here.
In order to see any DUNs error codes, you must dial from the 'Manage Network Connections' Window.
ALSO SEE: Connectoids. In many cases, DUNs Errors can be solved by correcting the properties for your dial-up networking connections.