Attempt to index number with 'HumanoidRootPart' error?

I have a code for a tower defense game. Unfortunately. Line 6 in the code below is giving me the error. Below is the code. (yes, there is more code, but this is only the part thats causing trouble)

function FindNearestTarget(newTower)
	local maxDistance = 15
	local nearestTarget = nil
	for i, target in ipairs(workspace.Mobs:GetChildren()) do
		print(newTower.HumanoidRootPart.Position)
		local distance = (target.HumanoidRootPart.Position -newTower.HumanoidRootPart.Position).Magnitude
		--print(target.Name, distance)
		if distance < maxDistance then
			nearestTarget = target
			maxDistance = distance
		end
	end

	return nearestTarget
end

Nevermind. It was an issue with calling the function later on in the script that provided the problem