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();

        }