If you look in your Mach3 / Bitmaps folder - the folder MillBitmaps contains all the images necessary for the standard screen 1024.set. When using any screen editor it has to be run from a location that can access both the screen and it's associated bitmaps folder otherwise, as you have found, images are missing from the editor screen.
I still use the old original editor but Klaus has produced a much improved editor together with instructional notes and video's on it's use;
http://www.kd-dietz.com/klausphp/pages/eng/machscreen/description/ms_description.htmlHope this helps,
Tweakie.