When you use Internet Explorer to access the http://companyweb Web site from a server that is running Windows Small Business Server 2003 with Service Pack 2, you may be prompted to provide your credentials. After you provide your credentials and then click OK for the third time, you receive the following error message:
HTTP 401.1 - Unauthorized
Note This problem occurs only if you access the Web site from the server. This problem does not occur if you access the Web site from a client computer.
According to Microsoft Knowledge Base article 896861, users receive this error message when the following conditions are true:
They make local NTLM authentication requests to a Web site that uses the NTLM authentication.
The Web site is hosted on Internet Information Services (IIS) 5.1 or IIS 6.
The Web site has a name that is mapped to the local loopback address.
The issue that is discussed in the "Symptoms" section triggers these conditions for the following reasons:
When you configure Windows Small Business Server 2003, the SharePoint Web site is automatically configured to use only the NTLM authentication. Therefore, Kerberos authentication is not enabled.
A static DNS record is created in the DNS database. The target host of the DNS record is the Fully Qualified Domain Name (FQDN) of the server.
Windows Internet Explorer 8 introduces a security improvement that expands the use of Service Principal Name (SPN) from the Negotiate authentication to include the NTLM authentication. This security improvement helps protect against credential reuse and helps protect the system from loopback attacks.
This update automatically enables the Kerberos authentication on the SharePoint Web site.
How to obtain this update
This update is available from the Microsoft Update Web site:
You must have .NET Framework 2.0 installed before you apply this update.
You do not have to restart the computer after you apply this update.
Update replacement information
This update does not replace a previously released update.
The English version of this update 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.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
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