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Users who currently operate either a Windows 95 or NT 4 based Networking System, may experience data corruption and system hang-ups when operating MS-DOS based applications over the Network. This problem exists on both dedicated File Server and Peer-to Peer configurations. Considerable corruption can occur spontaneously without warning and can render valuable data unusable without expert software engineering attention.
The solution is in three parts.

Solution Part I

The problem all along was in the vredir.vxd (virtual redirector) system file shipped with Windows 95 (even with Service Pack 1), and Windows 95 0SR2. It is buggy and the previous tech note quoted above (Q165966) is erroneous. Microsoft have released a new version of VREDIR.VXD (4.00.1116) and VNETSUP.VXD (4.00.1112) that eliminate the problems with the local cache (as well as other problems).

You can download the new versions from this page by clicking on the following file vrdrupd.exe

The file is 215,728 bytes in length. When run it starts up a standard setup to install the new    vredir.vxd (156,773 bytes, dated 11-Sep-97 11:16 am) and the new vnetsup.vxd (17,595 bytes, dated  30-May-97 11:12 am).

(Note: to find out the version of your VREDIR.VXD file you can do the following. Start up Explorer, find the file in \WINDOWS\SYSTEM and right click on it. Select Properties and then click on the Version tab. The version of the file is the top item.) You'll have to reboot your Windows 95 system to complete the installation.

Solution Part II

The next step is to add a new registry entry to the Windows 95 system, using Windows 95's REGEDIT.EXE.

Key: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\VREDIR
Value: DiscardCacheOnOpen (binary value)
Data: 01

Walk down the key tree until you reach the VREDIR subkey. Right click on the right hand pane, select New then Binary value. Enter the identifier DiscardCacheOnOpen and press Enter. Double click on the new identifier and a dialog is shown where you can enter the data  01.

Once you've exited REGEDIT, you will need to reboot your machine for the new setting to take effect. Only the new VREDIR.VXD will understand this setting, previous ones will ignore it.

Solution Part III

If you are using a Windows NT 4 server as your file manager (in other words, the shared data files reside on a Windows NT 4 server machine), there's one more step to take: You need to turn off optimistic locking at the server. You need to add a new registry key on the Windows NT 4 Server  (or modify the current one if it exists).

Key: HKEY_LOCAL_MACHINE\System\CurrentControlSet\services\LanmanServer\Parameters
Value:  EnableOpLocks (DWORD value)
Data: 0