AI sight system erroring for no apparent reason?

I've recently been working a game that needed a smarter AI, and the only one I could find has one function that always errors for me, even though I directly copied it after it errored the first time, it still errors though

this is a normal script in a model in the workspace

function CheckSight(target)
    local ray = Ray.new(MyRoot.Position, (target.Position - MyRoot.Position).Unit * 40)
    local hit,position = workspace:FindPartOnRayWithIgnoreList(ray, (script.Parent))

    if hit then

        if hit:IsADescendentOf(target.Parent) and math.abs(hit.Position.Y - MyRoot.Position.Y) < 2 then
            print("visible")
            return true
        end
    end
    return false
end

it always says "unable to cast object to value", but it worked just fine for the guy who made the original script.

so if anyone has any idea why its erroring, please tell me, I'm trying to have the game out this year (bad idea, but it was my brother's idea not mine)