I really don't know, but here is what I would try if I had this problem:
- temporarily rename the folders env, models, scripts, sound, textures
- temporarily rename the map itself
- don't calc the VIS and LIGHT phase
- try a different Trem program (I use TJW backport, I'd fall back to the original client or an alternative backport)
All this is not to fix the error but to find out what might be causing it.