The sendkeys code below works well for Notepad but it doesn't work for Calculator. What is the problem? (It's another problem compared to what I sent here http://stackoverflow.com/questions/2604486/c-sendkeys-problem)

[DllImport("user32.dll", CharSet = CharSet.Unicode)]
public static extern IntPtr FindWindow(string lpClassName,string lpWindowName);
[DllImport("User32")]
public static extern bool SetForegroundWindow(IntPtr hWnd);
private void button1_Click(object sender, EventArgs e)
{
    IntPtr calculatorHandle = FindWindow("SciCalc", "Calculator");
    //IntPtr calculatorHandle = FindWindow("Notepad", "Untitled - Notepad");
    if (calculatorHandle == IntPtr.Zero)
    {
        MessageBox.Show("Calculator is not running.");
        return;
    }
    SetForegroundWindow(calculatorHandle);
    System.Threading.Thread.Sleep(1000);
    SendKeys.SendWait("111*11=");
    //SendKeys.SendWait("{ENTER}");
    //cnt++;
    SendKeys.Flush();
}