Microsoft KB Archive/252299

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RAS Service Cannot Receive Calls over the COM Port After Reconnecting Cable

Article ID: 252299

Article Last Modified on 11/1/2006


  • Microsoft Windows NT 4.0 Service Pack 3
  • Microsoft Windows NT 4.0 Service Pack 4
  • Microsoft Windows NT 4.0 Service Pack 5
  • Microsoft Windows NT 4.0 Service Pack 6
  • Microsoft Windows NT 4.0 Service Pack 6a

This article was previously published under Q252299


If you disconnect and reconnect a modem cable and a you receive a call within a few seconds, the RAS service could lose the COM port. Other calls coming over that COM port are not answered by the RAS service.

These problems also occur on RRAS.

A RAS client (X.25) connects and disconnects in the middle of the call, after a few tries RAS Service loses the COM port and does not receive any calls.


This issue can occur if your computer has other kernel mode drivers that do COM port emulation.

RAS/RRAS does not check if a call is in progress when posting a listen command.


A supported fix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Apply it only to computers that are experiencing this specific problem.

To resolve this problem, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information about support costs, visit the following Microsoft Web site:

NOTE: In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

The English-language version of this fix should have the following file attributes or later:


  Date       Time     Size    File name     Platform
  01/18/2000 12:47p   71,440  rastapi.dll   Alpha
  01/18/2000 12:47p   35,600  rastapi.dll   i386


  01/25/2000 05:55p   70,928  rastapi.dll   Alpha
  01/25/2000 05:56p   35,600  rastapi.dll   i386

To work around this issue, stop and restart the RAS service.


Microsoft has confirmed that this is a problem in Windows NT 4.0.

Keywords: kbhotfixserver kbqfe kbbug kbfix kbnetwork KB252299