Technical support memos


September 9, 1998
Networking WIN95 PC's to Microsoft networking servers (WIN NT, WIN 95 peer server, etc.) - Microsoft redirector problem (VREDIR.VXD)
Anthony J. Frates (Copyright 1998 Addsum Business Software, Inc.)

Users on Microsoft networking platforms may experience data file integrity corruption, data file locking, program "hanging" and related problems due to problems in Microsoft's network redirector. (This issue is not specific to Btrieve or any other data file format but applies to any application that runs from or "under" WIN 95 and which shares files on a Microsoft network server such as another WIN95 PC or a WIN NT PC.)

When accessing information on a Microsoft networking server, the WIN95 network redirector (VREDIR.VXD) by default caches data locally for files that are accessed. If either the file size or the modified time does not change within a two second interval, the redirector will read information from the local cache rather than the file on the server. By reading the cached version instead of physically re-reading the file from the server, the latest record information that may have since been updated by another user on the network will not be retrieved and the subsequent integrity of the data file could then be placed into jeopardy. This problem exists in VREDIR.VXD dated prior to 2/11/97. Another, earlier problem with the network redirector occurred because a routine that unlocks and holds a new pending lock in the redirector program did not work correctly in a multithreaded environment. A program might, with that older version, appear to stop responding or give an error message that a data file could not be locked.

Without the VREDIR update and appropriate registry changes, one user could overwrite the posting of another or two users might be allowed to use a data file at the same time without the system issuing a conflict message. New customers, vendors, employees or other records could be lost. Record locking might not occur as it should or a PC could lock-up while posting corrupting data.

Microsoft has an update at:

The file is 215K bytes long. It has new versions of VREDIR.VXD (9-11-97) and VNETSUP.VXD (5-30-97). You will also have to add a registry entry to your 95 machines (this entry will turn off caching at the local PC but only the newer VREDIR will understand it - use REGEDIT to make the change - this next step is not included in Microsoft's knowledge base but is well documented elsewhere):

Binary Value Data=01

 If you are using a Windows NT 4 Server as the file manager (i.e. the shared data files reside on a Windows NT 4 Server machine) first turn off optimistic locking at the server and then add a new registry key on the NT 4 Server (or modify the current one if it exists):

Value=EnableOpLocks Dword
Value Data=0

Make these changes to every WIN 95 and NT 4 Server PC on the network. WARNING: using the Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall your operating system to correct them - proceed with caution! We recommend that you back-up your SYSTEM.DAT and USER.DAT registry files before attempting to make the changes (these are hidden files in your \WINDOWS\SYSTEM directory).

While unrelated to the redirector problem, ensure also that in the Network section of each WIN 95 PC's control panel settings that only those network components that are required are listed; especially check protocols and client settings. Remove any and all IPX/SPX protocols unless there is a specific reason for them to be there (IPX/SPX can cause Btrieve to hang in a non-Novell environment; for example see Microsoft knowledge base article Q150567). Unless a Novell server also exists on the network, no Novell client drivers should be present.

Relevant Microsoft knowledge base articles relating to this issue include: Q165403, Q148367, and Q142803

Another web site with related information is:

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Technical support phone number: 801-277-9240