Important This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:
256986 Description of the Microsoft Windows Registry
When you try to use a virtual private network (VPN) connection on a Microsoft Windows Server 2003-based computer, you may receive the following error message:
Error 633 - the modem (or other connecting device) is already in use or is not configured properly.
This issue may occur if the TCP port that is used by the VPN connection is already being used by another program. The VPN connection uses TCP port 1723 to establish a connection. If another program is already using this port, you cannot establish a VPN connection.
Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk. To work around this issue, use one of the following methods:
Explicitly reserve the TCP port that is used for the VPN connection. To do this, follow these steps:
Click Start, click Run, type regedit.exe in the Open box, and then click OK.
In Registry Editor, locate and then click the following registry subkey: