Applies To:
  • CitectSCADA


This article has been superseded by article Q4627  - 'A Client/Server Connection is not Re-established after a Network Failure on Windows 2000/XP'.

A client/server connection is not re-established after a network failure when using NetBIOS over TCP/IP on Win2000 machines.

This will occur if a Win2000 machine being used as a display client or I/O Server has it's network cable removed, all display values on the client or any client scanning the I/O Server will display #COM due to the broken connection, however when the network cable is replaced these display values will remain in the #COM state. Citect on the machine that has had it's network cable removed must be restarted before data will be displayed again.


This problem is specific to Win2000 machines using TCP/IP and is due to the Win2000 "Media Sensing" feature.

To correct this problem Citect automatically disables the Media Sensing feature when installed on a Win2000 machine.

The Media Sensing feature can be re-enabled in the following manner,

1. From the start menu select Run, and open Regedt32.exe.

2. Use the Registry Editor to view the following key in the registry:


Remove the following registry value:

Value Name: DisableDHCPMediaSense

3. Restart the computer.

WARNING  Re-enabling this feature when using NetBIOS over TCP/IP on a Win2000 machine will prevent Citect being able to re-establish a network connection after a network failure. Citect will have to be restarted on a machine that loses it's network connection.