System Error 85 with "NET USE" Command (253821)

IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

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

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

Change the entry for

HKLM\System\CurrentControlSet\Control\SessionManager\ProtectionMode

from 1 to 0.