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A Cautionary Tale

by Stephan Grieger and Ross Mack - GUI Computing
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We had a most interesting problem recently, which involved a rather weird situation whereby a given Win95 PC refused to read an Access MDB via ODBC. Not so unusual? Well, what made it a bit weirder was the fact that, if someone else opened the file first then closed it, everything suddenly started to work. Very strange… some investigation ensued and we also noted that a number of Win95 machines were reporting problems with SHARE.EXE when opening ODBC connections to the database. We also noted that the database in question resided on a Netware server that had a drive mapped to it for access to the MDB. Things were beginning to fall into place.

The drive had been mapped using the Netware software (as part of the login processing). When the drive was re-mapped using Win95 it worked perfectly, and additionally no SHARE.EXE errors were reported.

Our theory (which certainly solved the problem in this case) is that the Netware redirector which is initially loaded does not correctly perform the file locking or permission checking that JET requests when opening/reading the file. Thus the SHARE errors and inability to read the file properly. When the drive is mapped with Win95, file system requests for that drive are then passed through the Win95 32bit Network redirector which knows how to respond correctly to all of JET's requests. Remember, even though the PC is using ODBC the ODBC driver manager loads JET to actually perform the data access.

When will people realise that Microsoft's client for Netware and IPX/SPX protocols that ship with Win95 (or NT...) are a whole lot more stable and compatible than the old NETX or VLM redirectors that they cling to like treasured childhood memories ?



Written by: Stephan Grieger Ross Mack
March '97

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