[Nisgeis]

Are you running any mods? Some change the ammo loadout so that there is no ammo of one particular type. I can't remember if it's HE or AP that is removed, but it's the default one and the result is that there is no ammo loaded when you click on the gun. If it is that problem, all you have to do is to click on one of the other shells on the deck gun screem to load that type. If it's not that, then I have no idea.