I have a BDC in a remote office. I usually use a DSL-based VPN connection through my ISP to connect the BDC to my corporate network. When my DSL connection goes down, I want to use a dial-up connection to link my BDC through a PPTP-based VPN to my company's Windows NT 4.0 server (which functions as a RAS server and a BDC). However, I can't make this connection work. I can dial in to the RAS server through a direct-dial connection, but when I try to connect to the PPTP server, I get a RAS 718 error. Can you help me?

First, make sure that all the servers are running NT 4.0 Service Pack 6a (SP6a), which fixed known problems that relate to the symptoms you describe. If the machines all run the most recent service pack, the problem might be a timeout on the PPTP session. Such a timeout can be a result of latency on the connection (for more information, see the Microsoft article "Troubleshooting PPTP Connectivity Issues in Windows NT 4.0" at http://support.microsoft.com/support/kb/articles/q162/8/47.asp).

The solution is to increase the number of attempts that PPTP makes to transmit data over the connection. Locate the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters registry subkey. If the PPTP-TcpMaxDataRetransmissions value (of type REG_DWORD) doesn't exist under this subkey, add the value, which has a range of 0 to 0xFFFFFFFF and a default of 9h.

The PPTPTcpMaxDataRetransmissions value controls the maximum number of times that the local system retransmits a PPTP packet when the remote host on the PPTP session doesn't acknowledge the packet. By design, this value's default is set higher than the default of 5h for the TcpMaxDataRetransmissions registry value, which specifies the maximum number of times that the local system retransmits an IP packet (and prevents unwanted dead-gateway detection on slow Internet connections). Still, you might need to further increase the default PPTPTcpMaxDataRetransmissions value on extremely slow connections.

First, try increasing the PPTP-TcpMaxDataRetransmissions value to 18h (i.e., 24 decimal), then reboot the server and retry the connection to see whether the 718 error persists. If the error still occurs, try increasing the value in increments of 1 or 2; however, keep in mind that Microsoft doesn't recommend increasing the value beyond 27h (i.e., 39 decimal).

If this problem is occurring over an ISDN connection that involves Motorola's BitSURFR Pro EZ ISDN modem, the problem might be device-specific. Refer to the Microsoft article "RAS Error 718 When Using Motorola ISDN BitSURFR Pro EZ" (http://support.microsoft.com/support/kb/articles/q181/5/46.asp) for information about resolving the problem.