"Missing texture 2 for material Normal"

I was going to try to finish my Temple arena today, but as soon as I re-exported the track and tried to test it, I was hit with the error message:
My build, assets, and exporter are up to date. Blender doesn't complain about any missing textures, and I tried copying all relevant images (including generic ones) into my track directory. It still doesn't work.
Anyone have any idea what this error message means, and just as importantly, how to fix the problem behind it?
- {l Code}: {l Select All Code}
[fatal ] STKMesh: Missing texture 2 for material Normal
My build, assets, and exporter are up to date. Blender doesn't complain about any missing textures, and I tried copying all relevant images (including generic ones) into my track directory. It still doesn't work.
Anyone have any idea what this error message means, and just as importantly, how to fix the problem behind it?