Symptoms
An unhandled exception may occur under the following circumstances: An ASP.NET worker process (Aspnet_wp.exe) runs under the default ASPNET account.
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You do not enable impersonation on that application.
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You try to connect to or write to an Access database. Under these circumstances, you may receive one of the following exceptions:

The Microsoft Jet database engine cannot open the file ‘C:\Nwind.mdb’. It is already opened exclusively by another user, or you need permission to view its data.

Operation must use an updateable query.
Resolution
Because of security concerns, the ASP.NET worker process runs under the default ASPNET account. If you do not enable impersonation for an application, all of the threads that run the requests for that application run under the process account.
This problem occurs because the ASPNET account does not have sufficient permissions to connect to or write to an Access database.