Please first check if there is a named instance of SQL Server called
“SQLEXPRESS” running on the host server. The error message indicates
that the specified server/instance is not valid. Please check if you
specify the correct server/instance
I noticed that you specify “user instance = true” in the connection
string. User instance is a feature of SQL Server Express and does not
supported by other editions of SQL Server like Enterprise or Standard.
If there is no SQL Server Express
instance on your host server, you need to attach the database to the
SQL Server instance and modify the connection string.
Please refer to the following link to attach databases: http://msdn.microsoft.com/en-us/library/ms190209.aspx
If it’s a default SQL Server instance, you can change the connection string to:
Data Source=.;Database=ASPNETDB;Integrated Security=True;
If it’s named instance, you can the connection string to:
Data Source=.\InstanceName;Database= ASPNETDB;Integrated Security=True;
For more information regarding the error and SQL Server user instance, please see: