What does this message mean?

I remade the system, added new things and changed it, but it always has that error. Now, prior to this happening, it was normal and fine. Then, I deleted the RSS files and emptied them in my recycle bin. Now, pretty much every new system I make cannot be played. Yes, I can open them up in planet studio but they won't be able to be played in the sandbox. It says that I need to start a new game through the file menu. Where do I find that? How do I fix this?