System.Data.SqlClient.SqlException: Failed to generate a user instance of SQL Server

Question

System.Data.SqlClient.SqlException: 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.

Anybody ever get this error and/or have any idea on it's cause and/or solution?

This link may have relevant information.

Update

The connection string is =.\SQLEXPRESS;AttachDbFilename=C:\temp\HelloWorldTest.mdf;Integrated Security=True

The suggested User Instance=false worked.

Answer 1

Here is the answer to your problem:

Very often old user instance creates some temp files that prevent a new SQL Express user instance to be created. When those files are deleted everything start working properly.

First of all confirm that user instances are enabled by running the following SQL in SQL Server Management Studio:

exec sp_configure 'user instances enabled', 1.
GO
Reconfigure

After running the query restart your SQL Server instance. Now delete the following folder:

C:\Documents and Settings\{YOUR_USERNAME}\Local Settings\Application Data\Microsoft\Microsoft SQL Server Data\{SQL_INSTANCE_NAME}

Make sure that you replace {YOUR_USERNAME} and {SQL_INSTANCE_NAME} with the appropriate names.

Source: Fix error "Failed to generate a user instance of SQL Server due to a failure in starting the process for the user instance."

Answer 2

You should add an explicit User Instance=true/false to your connection string