An unhandled exception may occur when you try to connect to an Access database from an ASP.NET worker process

An unhandled exception may occur under the following circumstances:

• An ASP.NET worker process (Aspnet_wp.exe) runs under the default ASPNET account.
  -and-
  
• You do not enable impersonation on that application.
  
  -and-
  
• You try to connect to or write to an Access database.

Under these circumstances, you may receive one of the following exceptions:

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.

To work around this problem, use one of the following methods:

• Configure the ASP.NET worker process to run under the SYSTEM account in the <processModel> section of the Machine.config file.
• For security reasons, Microsoft recommends that you enable impersonation on your ASP.NET application. This method works if the impersonated user has necessary permissions to the computer and the database that you are accessing.
• Grant read and write permissions for the "Everyone" group on the database and the database folder. This method is not safe; therefore, Microsoft does not recommend this method.

This behavior is by design.

When you need unlimited users, full-time support, and ACID transactions, Microsoft strongly recommends that you use Microsoft SQL Server with Microsoft Internet Information Services (IIS). Although Microsoft Active Server Pages (ASP) works with any OLE DB-compliant or ODBC-compliant database, IIS has been extensively tested. IIS is designed to work with Microsoft SQL Server on high transaction traffic and with unlimited users, which can occur in an Internet scenario.

Note "ACID" is an acronym for the four properties of transaction-processing systems: Atomicity, Consistency, Isolation, Durability.

ASP supports the use of the Microsoft Jet database engine as a valid data source. However, Microsoft ODBC Driver for Access and Microsoft OLE DB Provider for Jet are not intended for use with high-stress, high-concurrency, full-time server applications (such as Web applications, commerce applications, transactional applications, messaging servers, and so on).

Steps to reproduce the behavior

1. Create a new ASP.NET Web Application project in Microsoft Visual C# .NET.
2. Add the following code to the "Declaration" section of your Web Form, which appears at the top of the Code window:

   using System.Data.OleDb;					

3. Add the following code to the Page_Load event:

       String myConn  ="Provider=Microsoft.JET.OLEDB.4.0;Data Source=C:\\Nwind.mdb;";
       String myQuery  = "Insert into Customers(CustomerID,CompanyName) Values ('aaaaa', 'aaaaa')";
   
       OleDbConnection cn = new OleDbConnection(myConn);
       cn.Open();
       OleDbCommand cmd = new OleDbCommand(myQuery, cn);
       cmd.ExecuteNonQuery();
       cn.close();
   					

4. Modify the connection string as appropriate for your environment.
5. Compile the project.
6. View WebForm1.aspx in your browser. Notice that you receive one of the above-mentioned exceptions.

For additional information, click the following article numbers to view the articles in the Microsoft Knowledge Base: For more information about the <processModel> section, visit the following Microsoft Developer Network (MSDN) Web site: