خطای 40 در ASP.NET چیست؟

[Genius_Kasra]

سلام کسی میدونه این خطا برای چی هستش؟

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)
sqlconnection من به این صورت هستش :
SqlConnection con = new SqlConnection("Data Source=(localhost);Initial Catalog=Northwind);");

DataSet dst = new DataSet();
string selectlink = "SELECT * From login";
SqlDataAdapter dat = new SqlDataAdapter(selectlink, con);
string insertpost = "insert into entry (username) VALUES (@a)";
SqlCommand cmd = new SqlCommand(insertpost, con);
cmd.CommandType = CommandType.Text;
cmd.Parameters.AddWithValue("@a",this.TextBox1.Text );

con.Open();
cmd.ExecuteNonQuery();
con.Close();

[HamidiFar]

Data Source=myServerAddress;Initial Catalog=myDataBase;User Id=myUsername;Password=myPassword;

Data Source=myServerAddress;Initial Catalog=myDataBase;Persist Security Info=True;User ID=myUsername;Password=myPasswordSample :


Data Source=.;Initial Catalog=Northwind;Persist Security Info=True;User ID=sa;Password=passData Source=. => Data Source=local sql server


http://blog.sqlauthority.com/2007/04/23/sql-server-fix-error-40-could-not-open-a-connection-to-sql-server/