Game crash when entering sandbox

Ok, so I built my first platform and model, then built an engine to put in it. After i built the engine I noticed the platform section had nothing listed in it, but the model was still there. I shut the game down and restarted, and every time I click on sandbox I get the error in the attachment. I have tried using the cleaner and reinstalling 3 times but nothing has fixed it. The scenarios work fine. Thanks