Sikuli error on launch

I am trying to execute my first sikuli script with Selenium. Trying to automate desktop application - windows 7

Followed all the steps correctly as mentioned in http://www.helpingtesters.com/web-automation-with-sikuli-and-selenium/ but I am getting error again and again. Plz check

java.lang.AssertionError: Widget desktop invocation failed.

Script I am running is:
import org.sikuli.script.FindFailed;
import org.sikuli.script.Pattern; //This is class, which will focus on images
import org.sikuli.script.Screen; //This is a class, which will focus on the screen

public class DemoSikuli {

      public static void main(String args[]) throws FindFailed{
      Screen screen = new Screen();
      Pattern image = new Pattern(D:\\images\\Sikuli.PNG);
      screen.click(image);}
}