Possible Data Corruption by Microsoft Client

Network Clients include a cache to enhance network performance (for more info on the basics of data-caches, see: Network Client-Cache).

If you work in a Multi-User environment, where users access simultaneously the same data-files, please be aware about a problem with the "Microsoft Network Client", as documented by Microsoft in article ID: Q148367 (http://support.microsoft.com/support/kb/articles/q148/3/67.asp)

Quote:

Symptoms

When you use the Microsoft Client for Microsoft Networks, a file on a Microsoft networking server (such as a Microsoft Windows NT, Windows95, Microsoft Windows for Workgroups, or Microsoft LAN Manager server) may become damaged or may contain invalid data if multiple workstations access the file at the same time.

Cause

The network redirector (VREDIR.VXD) caches data locally for files it accesses on a Microsoft networking server. If the file size does not change or if the last modified time does not change within a two-second period, the redirector reads file data from the locally stored cache rather than from the file on the server.

Resolution

This issue is resolved by the following updated file for Windows95:
VREDIR.VXD version 4.00.1112 (dated 2/11/97) and later
The following file is available for download from the Microsoft Solftware Library:
vrdrupd.exe (size: 215728 bytes)

another knowledge base article on a similar subject: Q174371:

Possible Database File Damage When Data Is Appended

SYMPTOMS

Database programs running in Windows 95 OEM Service Release 2 (OSR2) or 2.1 (OSR 2.1) over a Microsoft network may damage the database.

CAUSE

When a program uses the GetFileSize() API to get the size of an existing file on a Microsoft networking server (such as a Windows NT-based server), the Client for Microsoft Networks may not return the correct file size. When the program then attempts to write additional information to the end of the file, it may overwrite existing data instead.

This problem has been observed only with the version of the Client for Microsoft Networks (Vredir.vxd) included with OSR2 (version 4.00.1111) and later.

STATUS

This issue is resolved by the following updated file for Windows 95 OSR2:

Vredir.vxd version 4.00.1116 (dated 9/11/97) and later

For the download of this patch, please look-up the Microsoft article Q174371, which includes the download link,
which was on my last visit: ftp://ftp.microsoft.com/softlib/mslfiles/vrdrupd.exe.

Which version do you have installed ?

	Use in the Start-Menu the "Find"-command to search for VREDIR.VXD. Once it is located, make a right-click on the name to call up the context menu and select Properties.
	Verify the size of the file.
	Verify the: - File version - Product version On my new Windows95 B, I do NOT have the proper version installed.

Installation of the patch:

	Download the file VRDRUPD.EXE (via Q148367 ) and run it.
	Agree to upgrade.
	It copies a few files and is quickly done. You need to reboot !

Verification of Installation:

	Use "Find" to search for VREDIR.VXD and look at its properties.
	The new version of VREDIR.VXD has 156.773 bytes
	The current download includes already the file version 4.00.1116