Weird lightmapping issue

Hi, I'm new to Unity so this may be something simple, but I can't find the answer anywhere.

I'm creating lightmaps for 2 different scenes (both racetracks) that uses the same prefabs, textures, UVs and everything else. The lightmap on the first scene worked fine, no error messages and decent resolution for what I needed. The second one refuses to work correctly and gives me the message:

"UV set on mesh is incorrect. Lightmapper needs UVs inside the (0,1)x(0,1) space."

The lightmap works fine on terrain and other objects, but it's all messed up, full of black and white spots on the track, tunnels and things close to it. But I used the exact same mesh on the first one! What's happening? How do I solve it? Thank you!