I'm working on adding thermal animation to my model, but when I load it into KSP, the game says the model is either invalid or missing. I removed the thermal animation in Unity and it worked fine, so that's definitely what's causing the problem. I read that someone else was able to solve this issue by using an older version of Unity, so I downgraded to the same version they said they switched to (version 4.2), yet strangely, the problem persists. My only thought is, is this an issue with Part Tools .23? Otherwise I'm totally confused why this doesn't work, even when I followed the guide posted on here to the letter...