I am running this situation, what are the factors

The application server error.
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in the establishment and server The connection error.Connect to the SQL Server 2005, the default settings SQL Server does not allow for the next long-range connections may result in the failure.(Provider:Named Pipes Provider, error:40 – not open to the SQL Server Connection)
:the implementation of the current Web request, the emergence of an unhandled exception.Please check stack trace information to learn more about the error code, as well as lead to the wrong source of information.

Unusual details :System.Data.SqlClient.SqlException:the establishment in connection with the server error.Connect to the SQL Server 2005, the default settings SQL Server does not allow for the next long-range connections may result in the failure.(Provider:Named Pipes Provider, error:40 – unable to open the SQL Server connection)

source of error:

line 21:string settings = Convert.ToString (ConfigurationManager.ConnectionStrings [ “SqlConnection” ]);
line 22:SqlConnection myconn = new SqlConnection (settings);
line 23:myconn.Open ();
line 24:string strsql = “insert into Users (UserName, UserPWD) Value ( “;
line 25:strsql = strsql +”'”+ tbxusername.Text +”'”;

Source:d:\ chy3 \ login.aspx.cs line:23

stack trace:

[SqlException (0x80131904):the establishment in connection with the server error.connect to the SQL Server 2005, the default settings SQL Server does not allow the next Remote connections may result in the failure.(Provider:Named Pipes Provider, error:40 – unable to open the SQL Server connection)]
System.Data.ProviderBase.DbConnectionPool.GetConnection (DbConnection owningObject) +437
System.Data.ProviderBase.DbConnectionFactory.GetConnection (DbConnection owningConnection) +82
System.Data.ProviderBase.DbConnectionClosed.OpenConnection (DbConnection outerConnection, DbConnectionFactory connectionFactory) +105
System.Data.SqlClient.SqlConnection.Open ( ) +111
Login.btnlogin_Click (Object sender, EventArgs e) in d:\ chy3 \ login.aspx.cs:23
System.Web.UI.WebControls.Button.OnClick (EventArgs e) +105
System.Web.UI.WebControls.Button.RaisePostBackEvent (String eventArgument) +107
System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent (String eventArgument) +7
System.Web.UI.Page.RaisePostBackEvent (IPostBackEventHandler sourceControl, String eventArgument) +11
System.Web.UI.Page.RaisePostBackEvent (NameValueCollection postData) +33
System.Web.UI.Page.ProcessRequestMain (Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +5102