VS 2008 Error When Open SqlConnection?

When i connection on database Microsoft SqlServer 2008 By This code.

Code:
SqlConnection cnn = new SqlConnection(ConfigurationManager.ConnectionStrings["myconnection"].ConnectionString);
SqlCommand cmd = new SqlCommand("select * from [City]", cnn);
cnn.Open();
Code In configration Manager
Code:

<add name="myconnection" connectionString="Data Source=.;Initial Catalog=db;Integrated Security=True;User Instance=True"
providerName="System.Data.SqlClient" />
found this Sql Exception:

The user instance login flag is not supported on this version of SQL Server. The connection will be closed. what is problem?