Microsoft KB Archive/933227

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Article ID: 933227

Article Last Modified on 10/31/2007


  • Microsoft .NET Framework 1.1


If an application that is built on the Microsoft .NET Framework 1.1 uses Kerberos credentials to authenticate, you intermittently receive the following error message:

HTTP 401 Unauthorized

This problem occurs if the following conditions are true:

  • The value of the HttpWebRequest.PreAuthenticate property is set to true.
  • A request that requires Kerberos authentication is sent after the time that is specified in the ServicePoint.MaxIdleTime property.


This problem occurs because of a bug in the .NET Framework 1.1. The System.Net.ServicePoint class manages the connections that the System.Net.HttpWebRequest class uses. If a ServicePoint object is idle for the time that is set in the ServicePoint.MaxIdleTime property, the object is deleted. Then, a new ServicePoint object is created for a request to the same URL. At the same time, an incorrect Service Principle Name (SPN) string is created because of a bug in the .NET Framework 1.1. The incorrect SPN causes the failure of Kerberos authentication if preauthentication is used. Then, the client application may use NTLM authentication. If the Web server cannot process NTLM authentication, the "HTTP 401 Unauthorized" error is returned to the client application.


Hotfix information

A supported hotfix is now available from Microsoft. However, it is intended to correct only the problem that is described in this article. Apply it only to systems that are experiencing this specific problem. This hotfix may receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next .NET Framework 1.1 service pack that contains this hotfix.

To resolve this problem immediately, contact Microsoft Customer Support Services to obtain the hotfix. For a complete list of Microsoft Customer Support Services telephone 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.


You must have the .NET Framework 1.1 Service Pack 1 installed to apply this hotfix.

Restart requirement

You do not have to restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

File information

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.

File name File version File size Date Time Platform SP requirement
Aspnet_isapi.dll 1.1.4322.2423 258,048 10-Aug-07 11:48 x86 SP2
Aspnet_wp.exe 1.1.4322.2423 32,768 10-Aug-07 11:48 x86 SP2
Corperfmonext.dll 1.1.4322.2423 81,920 10-Aug-07 11:48 x86 SP2
Mscorie.dll 1.1.4322.2423 86,016 10-Aug-07 11:49 x86 SP2
Mscorjit.dll 1.1.4322.2423 315,392 10-Aug-07 11:49 x86 SP2
Mscorld.dll 1.1.4322.2423 102,400 10-Aug-07 11:49 x86 SP2
Mscorlib.dll 1.1.4322.2423 2,142,208 21-Aug-07 3:10 x86 SP2
Mscorsn.dll 1.1.4322.2423 77,824 10-Aug-07 11:49 x86 SP2
Mscorsvr.dll 1.1.4322.2423 2,523,136 10-Aug-07 11:49 x86 SP2
Mscorwks.dll 1.1.4322.2423 2,514,944 10-Aug-07 11:50 x86 SP2
Setregni.exe 1.1.4322.2034 106,496 20-Aug-07 11:06 x86 SP2
Sy52106.dll 1.1.4322.2423 1,232,896 3-Aug-07 8:59 x86 SP2
System.web.dll 1.1.4322.2423 1,265,664 3-Aug-07 8:59 x86 SP2


To work around this problem, set the value of the HttpWebRequest.PreAuthenticate property to false.


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.


For more information about how to set the value of the HttpWebRequest.PreAuthenticate property, visit the following Web site:

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates

Additional query words: HttpWebRequest SPN Kerberos PreAuthenticate 401 HTTP Unauthorized

Keywords: kbexpertiseadvanced kbfix kbpubtypekc kbqfe kbhotfixserver KB933227