System.Data.SqlClient.SqlException: An error has occurred while establishing a connection to the server. When connecting to SQL Server

frnt end : asp.net framework 3.5

back end : sql server 2005

operating system :windows xp

error is

Server Error in '/Employee' Application.
________________________________________
An error has occurred while establishing a connection to the server.  When connecting to SQL Server 2005, this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.Data.SqlClient.SqlException: An error has occurred while establishing a connection to the server.  When connecting to SQL Server 2005, this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)

Source Error: 

Line 82:         catch (Exception e)
Line 83:         {
Line 84:             throw e;
Line 85:         }
Line 86:         finally

Source File: d:\Employee\App_Code\Marvel.cs    Line: 84 

Stack Trace: 

[SqlException (0x80131904): An error has occurred while establishing a connection to the server.  When connecting to SQL Server 2005, this failure may be caused by the fact that under the default settings SQL Server does not allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)]
   Marvel.GETDS(String qry) in d:\Employee\App_Code\Marvel.cs:84
   EmployeeRegistration.TextBox1_TextChanged(Object sender, EventArgs e) in d:\Employee\EmployeeRegistration.aspx.cs:90
   System.Web.UI.WebControls.TextBox.OnTextChanged(EventArgs e) +1234972
   System.Web.UI.WebControls.TextBox.RaisePostDataChangedEvent() +52
   System.Web.UI.WebControls.TextBox.System.Web.UI.IPostBackDataHandler.RaisePostDataChangedEvent() +7
   System.Web.UI.Page.RaiseChangedEvents() +117
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1646

________________________________________
Version Information: Microsoft .NET Framework Version:2.0.50727.1433; ASP.NET Version:2.0.50727.1433