close Event for Onscreen keyboard on button click event

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C#2.0

C#

C#4.0

C#3.5

I have created one on-screen keyboard with button click event..
This function is called or run onscreen key board.....

private void loginControl1_btnOnScreenProcessKeyboardUser(object sender, EventArgs e)
       {
           if (p == null)
           {
               string Pproccename;
               pid = 0;
               p = System.Diagnostics.Process.Start("osk");
               pid = p.Id;
               Pproccename =  p.ProcessName.Trim();
           }
           else
           {
               p.Kill();
               p.Dispose();
               p = null;
           }
       }

Now I have closed that process with that function or that code

 if (p1id > 0)
//if (p1 != null)
{
    p1.Kill();
    p1.Dispose();
    p1 = null;
}
else if (pid > 0)
// else if (p != null)
{
    p.Kill();
    p.Dispose();
    p = null;
}

It should work to close screen keyboard...
but when you click keyboard close directly then it gives error.. so tell me what should I do?
Give me answer...