Unable to cast string to bool, What?

I'm making a game and I have ran into an error I don't understand Unable to cast string to bool

here's the script:

game.ReplicatedStorage.Remotes.BuyDance.OnServerInvoke = function(plr, Up, Down, Left, Right)

local animation = game.ReplicatedStorage.Animations:FindFirstChild(Up, Down, Left, Right)

if plr.leadersats.Points.Value >= animation.Price.Value then
    if not plr.playerValues.Animations:FindFirstChild(Up, Down, Left, Right) then
        plr.leaderstats.Points.Value -= animation.Price.Value

        local valUp = Instance.new('StringValue', plr.Animations)
        local valDown = Instance.new('StringValue', plr.Animations)
        local valLeft = Instance.new('StringValue', plr.Animations)
        local valRight = Instance.new('StringValue', plr.Animations)
        valUp.Name = Up
        valDown.Name = Down
        valLeft.Name = Left
        valRight.Name = Right

        plr.playerValues.UpAnimation = Up
        plr.playerValues.DownAnimation = Down
        plr.playerValues.LeftAnimation = Left
        plr.playerValues.RightAnimation = Right


        return 'Success'
    else
        plr.playerValues.UpAnimation = Up
        plr.playerValues.DownAnimation = Down
        plr.playerValues.LeftAnimation = Left
        plr.playerValues.RightAnimation = Right

        return 'Equip'
    end
else
    return 'Error'
end

end