Having the same problem! For a while it still worked fine when I loaded in (except for the invisible floor), but now it's giving me this error too. I even have the zm nuked actor on the map.... so confused

In radiant, all of my textures/terrains show up fine, lighting is great, but when I run the map, I have no walls, ground, floor, etc. All models, fx, structs, etc are still there. The only other thing not working is that I can't knife zombies, and they can't hit me. Shooting them works fine, but that's about it.

When compiling/linking, I get there error:
WARNING: NavVolume generation is skipped. Flying units might not behave correctly. This might be due to there is no nav_volume brush in the level, or the generation is skipped purposely by skipping -navvolume option.

However, from what I've read, this shouldn't make a difference. What am I doing wrong?