System Error 85 with "NET USE" command

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Article ID: 253821
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Symptoms

When a non-administrative user attempts to reconnect to a shared network drive that the user has already used, system error 85 ("Local device name already in use") may be generated.

For example, running the following sequence of commands in a logon script or from a command prompt illustrates the issue:
net use r: /d
net use r: \\servername\share
net use r: /d
net use r: \\servername\share
The behavior does not occur for users with administrative privileges.

Cause

This behavior is caused by a setting of 1 in the following registry value:
HKLM\System\CurrentControlSet\Control\SessionManager\ProtectionMode
If the setting is 1, the problem occurs. If you change the setting to 0 and reboot the server, the problem disappears.

Note that the following articles in the Microsoft Knowledge Base suggest changing this value to 1 to restrict changes to Base System objects and for solving problems with symbolic links:
218473 Restricting Changes to Base System Objects
244995 Base System Object Restrictions Are Not Enabled by Default
222159 Symbolic Link Case Sensitivity Exploit Bypasses System Security

Workaround

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 How to back up and restore the registry in Windows

Change the entry for
HKLM\System\CurrentControlSet\Control\SessionManager\ProtectionMode
from 1 to 0.

Note If you are running a Windows Server 2003-based Terminal Server, set the ProtectionMode to a value of 1. "Error 85" translates to the following:
ERROR_ALREADY_ASSIGNED "The local device name is already in use."
For more information, click the following article number to view the article in the Microsoft Knowledge Base:
935642 Error message and the terminal server roaming profile is not loaded when you log on to a Windows Server 2003-based terminal server

Properties

Article ID: 253821 - Last Review: June 19, 2014 - Revision: 4.0
Keywords: 
kbenv kberrmsg kbprb KB253821

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