I have been trying to move some map objects into base.rte/index so that I can used them in the map creator. I put in the following:

IncludeFile = BW.rte/Maps/BG.ini
IncludeFile = BW.rte/Maps/Materials.ini
IncludeFile = BW.rte/Maps/Objects.ini
IncludeFile = BW.rte/Maps/Terrains.ini

and I commented out their spot in their original files

I get the error "assertion failed: Tried to make a material mapping in an official or out-of-bounds datamodule!"

What am I doing wrong?

What files exactly did you move into Base.rte?

Also this should be in Support.

It does that when you try to make more materials outside base's materials.ini while it reads base's index.ini.