getting error in Image Croping function

Hello,
I am trying to call a static function cropImage here is how it looks..

  public static Image CropImage(Image img, Rectangle cropArea)
     {
            logic goes here..
     }

I want to call this fuction to crop am image how can i do this,
When i tried like this

Rectangle objRect=new Rectangle(20,10,200,100);
    static_className.CropImage(image,objRect);

I got an error saying invalid argument.

Thanks & Regards,