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LMCompatibilityLevel and Its Effects

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Article ID:175641
Last Review:January 22, 2007
Revision:3.2
This article was previously published under Q175641

SYMPTOMS

When you try to connect to down-level clients on a computer running Windows for Workgroups and Windows 95, you may receive the error message:
\\Server\Share is not accessible.
-or-
System Error 50 has occurred.
The Network Request is not supported.
This message appears when you connect to a Windows 95 computer that has been set up to use User Level Access Control and when you connect to a share that has a password (Read or Full Control) set on it.

Setting LMCompatibilityLevel to 2 prevents a Microsoft Exchange Server 4.0 and 5.0 client from gaining access to a Microsoft Exchange Server versions 4.0 and 5.0 from the Inbox with one of the following error messages:
Microsoft Exchange Server

Your Microsoft Exchange Server is unavailable.

You can retry connecting to the server using the network, or work offline and connect using dial-up networking.

Network problems are preventing connection to the Microsoft Exchange Server computer. Contact your system administrator is this condition persists.
-or-

Microsoft Exchange Server

The logon credentials supplied were incorrect. Make sure your username and domain are correct then type your password again.

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CAUSE

If LMCompatibilityLevel is set to 2, Windows NT will never send a LANMAN challenge/response, and Windows NT will be unable to connect to clients that require it.

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MORE INFORMATION

To increase password security, Windows NT 4.0 allows you to restrict the sending of LANMAN challenge/response passwords over the network. This may, however, make Windows NT unable to connect to down-level clients and Exchange 4.0 and 5.0 clients.

For additional information on preventing the sending of LANMAN passwords, click the article number below to view the article in the Microsoft Knowledge Base:
147706 (http://support.microsoft.com/kb/147706/EN-US/) How to Disable LM Authentication on Windows NT

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RESOLUTION

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
152734 (http://support.microsoft.com/kb/152734/EN-US/) How to Obtain the Latest Windows NT 4.0 Service Pack

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APPLIES TO
•Microsoft Windows NT Workstation 4.0 Developer Edition
•Microsoft Windows NT Server 4.0 Standard Edition
•Microsoft Windows for Workgroups 3.2
•Microsoft Windows 95
•Microsoft Exchange Server 4.0 Standard Edition
•Microsoft Exchange Server 5.0 Standard Edition
•Microsoft Exchange Server 5.5 Standard Edition
•Microsoft Exchange Windows NT client
•Microsoft Outlook 97 Standard Edition, when used with:
  Microsoft Windows 95
  Microsoft Windows 98 Standard Edition
  Microsoft Windows 98 Second Edition

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Keywords: 
kbbug kbfix KB175641

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