Somehow, this line has made it in to the project XML for the sprite "gold" object's "initial visibility" property:
initial-visibility>undefined</initial-visibility>
That should say one of the two options: "Visible" or "Invisible". I have no idea how it could end up with "undefined", it's not an option in the list! Any ideas what you were doing that led to this happening, in particular with that property?
You can work around it by selecting all "gold" objects and selecting "visible" for the "initial visiblity" property again. Then it fixes it (it's no longer "undefined").