This will be an error in either 3 scripts or as simple as you don't have a weapon checked in ur mods builder. If this is a custom weapons that is either ported or from mutiplayer you must add the xmodel in the mod.cvs and the sounds
Ex).
xmodel,bo1_m1911_world
xmodel,bo1_m1911_view
sound,sp/bo1_m1911
(the sound .csv may be changed if you want so all sounds are in 1 file to keep your mod.csv clean)
Scripts the error could be in:
_zombiemode_weapons.gsc
_loadout.gsc
_dlc3_code.gsc
if you need help skype: derek_caudle