Hiya Clyde,
When you run PixelCNC what’s it say on the very top of the window? Does it just say PixelCNC or “PixelCNC (Trial)”? The examples included with the trial should all work just fine for the trial. The samples included with the full version will not work with the trial version of PixelCNC. The latest version right now is v1.18a, so if you don’t already have that version go ahead and grab it real quick: http://deftware.itch.io/pixelcnc/
EDIT: The free trial is limited to ~65,000 pixels on the image input, which means about a 256x256 (or any dimensions which multiply to 65k or less) will work on there.