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LMCompatibilityLevel and Its Effects

This article was previously published under Q175641
Retired KB Content Disclaimer
This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.
When you try to connect to down-level clients on a computer running Windowsfor Workgroups and Windows 95, you may receive the error message:
\\Server\Share is not accessible.
System Error 50 has occurred.
The Network Request is not supported.
This message appears when you connect to a Windows 95 computer thathas been set up to use User Level Access Control and when you connect to ashare that has a password (Read or Full Control) set on it.

If LMCompatibilityLevel is set to 2, Windows NT will never send a LANMANchallenge/response, and Windows NT will be unable to connect to clientsthat require it.
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.

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 How to Disable LM Authentication on Windows NT
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 theMicrosoft Knowledge Base:
152734 How to Obtain the Latest Windows NT 4.0 Service Pack
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Article ID: 175641 - Last Review: 04/26/2011 15:52:00 - Revision: 1.1

  • Microsoft Windows NT Workstation 4.0 Developer Edition
  • Microsoft Windows NT Server 4.0 Standard Edition
  • Microsoft Windows 95
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