Why do have an add-on under the name "Gamemode_Slayer (1).zip"?
Try re-downloading it. If that doesn't work, give us the link for it.
noedit: This also happens with all other weapons (excluding shotguns because they fire multiple rounds anyway, but the ammo still counts two rounds)
Does this actually happen with all weapons (including default) or just ones programmed to have limited ammo?
Are you sure you are using the weapon package specified for those scripts? The old H&K add-on package, which has a lot of weapons, doesn't require those support add-ons.