It has something to do with adding in the DTW walls. I wouldn't know how to fix it. I'll see if z3n knows.
Can you tell me what your export descr buildings looks like for building defenses?
Btw, it was Christmas holiday's so I was away for some time.
edit:
It could also be descr_engines/skeleton you need to look at, along with descr_walls, it seems like you're missing some of the code.
;EASTERN SMALL STONE/TOWN WALLS
wall
{
culture eastern carthaginian egyptian
level 3
siege_tower_size medium
straight
{
eastern_town_wall_straight
breach_inner_link 0 10
breach_outer_link 0 -10
breach_width 10
}
Also here's a list of files involved with walls.
data\descr_building_battle.txt
data\descr_engines.txt
data\descr_walls.txt
data\descr_building_battle\dbb_walls_*culture*.txt
data\descr_items.db
data\descr_items.txt
data\descr_items\di_*.txt
data\descr_projectile_new.txt
data\descr_oil_effect.txt