Why does it say unable to cast value to object?

Here is my script:

local region = Region3.new(Vector3.new(script.Parent.Reg1.Position), Vector3.new(script.Parent.Reg2.Position))

while true do
    wait()
    local touching = game.Workspace:FindPartsInRegion3(region, 1000)
    for i,v in pairs(touching) do
        if v.Parent:FindFirstChild('Humanoid') and v.Parent:FindFirstChild("HInfect") then
            local number = math.random(1,10)
            if number == 1 then
                v.Parent.HInfect:Destroy()
            else
                v.Parent.Humanoid:TakeDamage(v.Parent.Humanoid.Health)
            end
        end
    end
end