Unity Build Crashes Once Characters Touches Ground

Hello! I'm a bit of any amatuer to game development, and am working on my first Unity game.

So, currently, I have a terrain, some buildings, grass, what have you, and the first person character controller. The problem is, no matter what platform I 'Build' to, the game loads, the world is fine, but as soon as the character touches the ground, the game crashes. In addition, upon launch, the bar at the bottom quickly fills with warnings about scrips being obsolete, and to use different ones. Is that something I have to manually code? I'm assuming that's whats causing the crashes. Or is there a way to automatically replace them?

Thanks!