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Q288323: Web Browsers Receive "HTTP 401.5" Using NT Challenge/Response

Article: Q288323
Product(s): Internet Information Server
Version(s): 4.0
Operating System(s): 
Keyword(s): 
Last Modified: 27-JAN-2002

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The information in this article applies to:

- Microsoft Internet Information Server version 4.0 
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SYMPTOMS
========

After you install Microsoft Windows NT Server Service Pack 6a, Web Browsers, you
can receive the following error message:

  HTTP 401.5
  Unauthorized: Authorization failed by ISAPI/CGI app.

This error can occur when Internet Information Server (IIS) is set to require
Windows NT Challenge/Response on a Web site or virtual directory.

CAUSE
=====

HTTP Keep-Alives are required for Windows NT Challenge/Response to work
properly. If the HTTP Keep-Alives Enabled check box has been cleared, the IIS
metabase has not been updated with the correct setting, and therefore,
Keep-Alives are still enabled. Windows NT Challenge/Response continues to work
properly.

After you install Windows NT Server Service Pack 6a, the metabase setting is
corrected to match the HTTP Keep-Alives Enabled check box. Because Windows NT
Challenge/Response requires HTTP Keep-Alives, the now disabled setting prevents
Windows NT Challenge/Response from working correctly.

RESOLUTION
==========

1. In the Internet Services Manager, right-click the Web site for which you want
  to enable Windows NT Challenge/Response, and then click Properties.

2. Click the Performance tab, and the click to select the HTTP Keep-Alives
  Enabled check box.

3. Click OK.

MORE INFORMATION
================

For additional information on Windows NT Challenge/Response, click the article
number below to view the article in the Microsoft Knowledge Base:

  Q102716 User Authentication with Windows NT

Additional query words: NTLM keep-alives sp6a AllowKeepAlive AllowKeepAlives

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Keywords          :  
Technology        : kbiisSearch kbiis400
Version           : :4.0
Issue type        : kbprb
Solution Type     : kbpending

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