Pastebin says my log is too big to paste otherwise I'd have that.
that seems to be happening alot with big packs.
what i could find was that something is going wrong with getting the textures from the stitcher, i'm working on a fix but i'm still digging a bit in the dark.
I spent a little bit of time polishing some of my updates/improvements to Anvilmapper I did a while back.
The main difference in the program itself is that my version can take the output directory and the block colours file as arguments when running the program. And just now I also improved the script I used to compile it, so that if you are on Linux you can compile it simply by running the compile.sh script. And I added an example bash script for running the program.