Error in accessing application settings

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.NET

forms

web.config

Hi
I have a windows application from which an web application is starting.

private void Home_Load(object sender, EventArgs e)
       {
           string url = string.Format("http://localhost:49916/Express/Login.aspx?yek@soh={0}", System.Configuration.ConfigurationSettings.AppSettings["HK"].ToString());

           Process.Start("IExplore.exe", url);
           this.Close();
       }

It is working fine in my source code.

I created a setup for this application.
And installed.. successful.. but when I tried to run the installed application.. it is throwing error like below.

System.NullReferenceException: Object reference not set to an instance of an object.
   at HospitalClient_App.Home.Home_Load(Object sender, EventArgs e)
   at System.Windows.Forms.Form.OnLoad(EventArgs e)
   at System.Windows.Forms.Form.OnCreateControl()
   at System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible)
   at System.Windows.Forms.Control.CreateControl()
   at System.Windows.Forms.Control.WmShowWindow(Message& m)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
   at System.Windows.Forms.ContainerControl.WndProc(Message& m)
   at System.Windows.Forms.Form.WmShowWindow(Message& m)
   at System.Windows.Forms.Form.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

If I change the line

Process.Start("IExplore.exe", url);

to

Process.Start("IExplore.exe","http://localhost:49916/Express/Login.aspx?yek@soh=6775228");

the installed program is running fine..

Can anybody help me in this regards...

Thanks in anticipation
Regards
Sri