I see nobody else has replied - I don't have a good answer but will tell you that I have had that error when I was trying different meshes and bodies and scene files. If there is a mis-match of some sort (but I cannot tell you what actually causes it) between them, that is one the common errors to get.
If you are modding by changing existing files, my best suggestion is to try and use base files that work together already (e.g. arena mesh, and bo_arena, and scn_arena.obj) to start with.
You might find that some of them will work ok with other file combinations, but not always. so that is the best way to start out - with compatible elements at the beggining.
PM me if this is not clear.
DE