Well, since you have already tracked down the weapon that is causing your turret mapping error for the Homeworld mod. (excellent work BTW). The only thing left for me to do is to answer your simple question.
I would say that the mod you are looking for is the Battle Star Galactic Mod.
In there, you should find a module colonial_cruiser_weapon_pew_pew.txt
unlockcost = 0
lockable = 0
armour_penetration = 35
blasttexture = "turret_blast_red.dds"
category = "WEAPONS"
classname = "SIM_BulletWeaponModule"
color = 1
cost = 113
crew_required = 4
damage = 20
description = "Pew pew pew, you're dead!."
fire_interval = 430
guiname = "A laser that goes pew pew"
height = 12.3
hitpoints = 100
icon = colonial_cruiser_weapon_autocannon_20mm_gatling.dds
min_range = 90
max_range = 1000
name = "colonial_cruiser_weapon_pew_pew"
optimum_range = 400
powerconsumed = 11
shield_penetration = 55
size = "CRUISER"
sound = data/sounds/Pew Pew.wav
soundvolume = 0.3
speed = 6
tracking_speed = 9.9
turret_sprite = "turret_auto_c2"
turretsize = 8.0
weight = 135
width = 4.2
slot_type = TURRET
uisortpos = 99999
For those that are wondering what riddle TheSauron has solved.
There is a weapon that goes pew pew, which is not restricted to any race and happens to have a turret map that asks for turret_auto_c2. As that turret designation is not a standard reference and the module is not restricted, then that particular weapon would crash any other mod or vanilla race for that matter.
For what its worth, I suggest the following:
If you head across to \Gratuitous Space Battles\data\installs
In that directory rename bsg.txt to bsg.off
(well, on my PC its this one)
That should fix your turret mapping error.
(Make sure you dont have any BSG ships saved)
Long Term Solution:
Restrict any modules in the Battle Star Galactic Mod which does not have a standard turret mapping name and is not already restricted to the BSG Mod.
For more information, on how to solve problems similar to this one, head here