ERROR! -- Has Anybody Experienced This?

I was putting together some landscape materials last night. Everything worked fine, compiled, and played properly. When I built lighting, the materials were wiped and I was given an error. Whenever I open the materials and instances, I just get lines of red text all over the preview. Now the engine won’t even start and just keeps crashing with the same errors.

Anyway, here’s the log. Looks like it says I’m using “Illegal Characters” (naming?), but I’ve literally done nothing out of the ordinary. In fact, this is a nearly-new project that I have hardly any content in. Any advice? Log is uploaded.