Error while running event flamethrower-fluid::on_init()
flamethrower-fluid/control.lua:3: attempt to index field 'flamethrower-ammo' (a nil value)
stack traceback:
flamethrower-fluid/control.lua:3: in function <flamethrower-fluid/control.lua:1>

Other mods?

Several, I'll give you a list tomorrow

None of them adds anything similar to this fluid

For combat I have Bob's warfare and Rampant Arsenal, mainly

Seriously, I have a lot of mods, what kind of mod could cause a crash with this one? I mean, combat mods, right?

From the error message, it looks like something is removing/replacing or renaming the flamethrower ammo item.

If you disable Flamethrower Fluid and then load normally, what is there in place of flamethrower ammo? If you hold one in your cursor and then issue the Lua command "/c game.print(game.player.cursor_stack.name)" (this will disable achievements, don't save afterwards) what does it say?

I think it is flamethrower ammo, from AAI:flame tank mod