Have not seen how to make this happen, but it's thankfully easy to recover (in case you or others need the info)
Just UnZIP the Capx file and add some random image into textures folder with the name ground_invisable.png
After that, you can start C2 by double clicking EnlightenLand.caproj ).
Now it should open normally on C2 and I'd expect editing/saving etc to work normally.