Failed to generate a user instance of SQL Server??

I use VS2005 & sql2005express to create a website, but it cannot to display data.

When I run it, I got such errors:

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.

My web.config file:

<add name="LocalSqlServer" connectionString="Data Source=.\SQLExpress;Integrated Security=True;User Instance=True;AttachDBFilename=|DataDirectory|aspnetdb.mdf"/>

When I change the User Instance=True to False, it works, but MSDN says it is not safe.

I searched the past threads, which writes "delete the folder C:\Documents and Settings\yy\Local Settings\Application Data\Microsoft\Sqlserver Data, it will work".

I try, but failed. What should I do??

have u resolved this error, I'm getting the same?