If you try to use a Microsoft Jet (Access) database from multiple instances of the same application either on the same computer or on different computers, you receive the following error message:
-2147467259 Error ODBC Microsoft Access Driver: The database has been placed in a state by an unknown user that prevents it from being opened or locked.
This error occurs with both the Microsoft ODBC Driver for Access and the OLE DB Provider for Jet.
To run an .mdb file by multiple instances, Jet makes use of a lock delay and retry interval. However, under high load conditions, you may exceed these intervals.
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For more information about the support options that are available and about how to contact Microsoft, visit the following Microsoft Web site:http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMSThe following workaround extends the retry delay for Jet so that you can use additional instances. However, it is not recommended that you use this workaround if a high number of updates are being formed; this workaround is intended only for reading databases.
You can add the following sample error handler to your code. Please note that this handler only works with ADO and uses the Sleep function, which you must declare in your general declarations section.
' Retry until MAX_RETRIES are hit to increment your error count.
errorcount = errorcount + 1
If errorcount < MAX_RETRIES Then
' Sleep a random amount of time, and retry the same operation.
Sleep Int(MAX_SLEEP_INTERVAL * Rnd) + 1
' Retries did not help. Show the error, and fall out.
MsgBox Err.Number & " " & Err.Description
This behavior is by design.
The above-mentioned workaround is only for read-only mode. Microsoft does not support placing Jet .mdb files under high user load. Microsoft strongly recommends that you use Microsoft SQL Server or Microsoft Data Engine (MSDE) instead of Access when high user loads (that is, more than 15 instances) are required or anticipated, especially when updating is required.
For more information about the Sleep function, refer to the MSDN Library documentation.