Have downloaded VS 2008 Express, SQL Server 2005 Express, and ASP.net Data Access Tutorials 1.  After creating a new web site
for the Data Access Tutorial 1, I also created the Northwind database in SQL Server 2005 Express by using the instnwnd.sql downloaded.
I tried to run the aspx pages in the Data Access Tutorial 1 website .  All aspx pages returned the following error msg.    

Failed to generate a user instance of SQL Server due to a failure in starting the process for the user instance. The connection will be closed.

 Reviewing the Database Explorer showed there are a NORTHWIND.MDF and a SqlExpress.Northwind.dbo.  I also created another basic data access
website to display the Customers table of the SqlExpress.Northwind database.  This website worked fine after I selected mixed authentication mode. 

The connection string of the SQL datasource for the ASP.net DataAccess Tutorial 1 is shown below. 

How do I solve the User Instance error for the SQL Server 2005 Express?  I kind of remember this website worked fine when I first created it as a 'File System' website with Windows authentication mode for SQL Server 2005 Express.

Jeffrey 

<add name="NORTHWNDConnectionString" connectionString="Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\NORTHWND.MDF;Integrated Security=True;User Instance=True" providerName="System.Data.SqlClient"/>

</connectionStrings>

Check http://blog.devstone.com/aaron/archive/2006/01/09/1425.aspx 

or same solution mentioned in http://www.emadibrahim.com/2007/06/08/failed-to-generate-a-user-instance-of-sql-server-due-to-a-failure-in-starting-the-process-for-the-user-instance-the-connection-will-be-closed/ 

What are your authentication settings in your web.config file in the folder of your application?

 To the best of my knowledge, the error has something to with the Northwind.mdf in App-Data folder, the so-called
user instance.  Am I right?  I kind of remember we can get rid of the Northwind.mdf in the App_Data folder and create
a new database connection to the Northwind database in the Management Studio.  The new aspx page has worked fine before. 

My question now is why we want to use user instance or database in App_Data folder?  Any advantage?  Where can I
read more information about User Instance?

TIA,
Jeffrey

I changed the Connection String in web.config to the standard database connection to the local SQLExpress.
The DataAccessTutorial 1 website now runs very well.