How do I handle this texture error in a keydown event?

I created a User Input Service event with particles, when I press the F key I should create a ball with the texture but it is giving error and I do not know how I put texture in it

This is My Script

game.Workspace.RainbowFlash.OnServerEvent:Connect(function(Player)
    local Character = Player.Character or Player.CharacterAdded:Wait()
    local Rb1 = Instance.new("Part")
    Rb1.Name = "Rb1"
    Rb1.Shape = Enum.PartType.Block
    wait(0.3)
    Rb1.Size = Vector3.new(0.2,5,2)
    Rb1.Material = Enum.Material.Neon
    Rb1.Anchored = false
    Rb1.BrickColor = BrickColor.Random()
    Rb1.CanCollide = false
    Rb1.Parent = Character
    Rb1.CFrame = CFrame.new(Character.LeftHand.Position)
    local tx = Instance.new("ParticleEmitter")
    tx.Name = "Texute"
    tx.Texture = "rbxgameasset://Images/a"
    tx.LightEmission = 0.6
    tx.Lifetime = 1
    tx.Rate = 500
    tx.Rotation = -180
    tx.RotSpeed = -150,260
    tx.Speed = 0
    tx.SpreadAngle = 0,0
    tx.Parent = Rb1
    local bv = Instance.new("BodyVelocity")
    bv.MaxForce = Vector3.new(math.huge,math.huge,math.huge)
    bv.Velocity = Character.HumanoidRootPart.CFrame.lookVector*70
    bv.Parent = Rb1

    wait(0.5)
    Rb1.Touched:Connect(function(hit)
        if hit and hit.Parent.Humanoid then
            hit.Parent.Humanoid:TakeDamage(5)
        end
    end)
    wait(1.5)
    Rb1:Destroy()
end)

Someone Help me