Why do i get this output (new is not a valid member)?

can someone help me

Material = "Grass"
InProgress = false
SpawnEnabled = false
BrickEnabled = false
TreeEnabled = false

local CoreGui = game:GetService("CoreGui")

self = PluginManager():CreatePlugin()
toolbar = self:CreateToolbar("RobloxMinecraftDK")
button = toolbar:CreateButton("","Baseplate Generator","Baseplate Generator Icon.PNG")
mouse = self:GetMouse()

local GuiCreated = false
local holderGui = Instance.new('ScreenGui',CoreGui)
holderGui.Archivable = false
holderGui.Name = "BGGui"
local holderFrame = Instance.new('Frame',holderGui)
holderFrame.Name = "BGFrame"
holderFrame.Style = "RobloxSquare"
holderFrame.Visible = false
holderFrame.Archivable = false
holderFrame.Size = UDim2.new(1,0,0,200)
holderFrame.BackgroundTransparency = 0
holderFrame.Parent = holderGui

function GenerateBaseplate()
    if InProgress == false then
        InProgress = true
        holderFrame.Generate.Text = "Generating"
        print "Running"
        local Brick = Instance.new("Part",game.Workspace)
        Brick.Anchored = true
        Brick.Name = "Baseplate"
        Brick.Size = Vector3.new(250, 0, 250)
        wait(0.1)
        Brick.Position = Vector3.new(0, 0, 0)
        wait(0.1)
        if SpawnEnabled == true then
            local Spawn = Instance.new("SpawnLocation",game.Workspace)
            Spawn.Anchored = true
            Spawn.Size = Vector3.new(6, 1.2, 6)
            wait(0.1)
            Spawn.TopSurface = "Smooth"
            Spawn.Position = Vector3.new(0, 1,2, 0)
            wait(0.1)
        end
        if Material == "Grass" then
            Brick.BrickColor = BrickColor.new("Camo") --Here
        elseif Material == "Sand" then
            Brick.BrickColor = BrickColor.new("Cool yellow") --Here
        elseif Material == "Ice" then
            Brick.BrickColor = BrickColor.new("Medium blue") -- Here
        end
        wait(0.1)
        local Decal = Instance.new("Decal",Workspace.SpawnLocation)
        wait(0.1)
        Decal.Face = "Top"
        Decal.Texture = "rbxasset://Textures/SpawnLocation.png"
        wait(0.1)
        Brick.Material = Material
        wait(0.1)
        if BrickBut == true then
            local BuildBlock = Instance.new("Part",game.Workspace)
            BuildBlock.Position = Vector3.new(14, 1.2, -32)
            wait(0.1)
            local Truss = Instance.new("TrussPart",game.Workspace)
            Truss.Position = Vector3.new(9, 1.6, -32)
            wait(0.1)
            local Wedge = Instance.new("WedgePart",game.Workspace)
            Wedge.Position = Vector3.new(5, 1.2, -32)
            wait(0.1)
            local CornerWedge = Instance.new("CornerWedgePart",game.Workspace)
            CornerWedge.Position = Vector3.new(1, 1.6, -32)
            wait(0.1)
            local Cylinder = Instance.new("Part",game.Workspace)
            Cylinder.Shape = "Cylinder"
            Cylinder.Position = Vector3.new(-4, 2.6, -32)
        end
        if TreeEnabled == true then
            Val = 0
            while true do
                wait(0.1)
                VectorX = math.random(-125,125)
                VectorZ = math.random(-125,125)
                local Wood = Instance.new("Part",game.Workspace)
                Wood.Size = Vector3.new(2,10,2)
                Wood.BrickColor = BrickColor.new("Reddish brown")
                Wood.Position = Vector3.new(VectorX,0,VectorZ)
                Wood.TopSurface = "Smooth"
                Wood:MakeJoints()
                wait(0.1)
                local Leaf = Instance.new("Part",game.Workspace)
                Leaf.Size = Vector3.new(10,10,10)
                Leaf.BrickColor = BrickColor.new("Bright green")
                Leaf.Position = Wood.Position
                Leaf.TopSurface = "Smooth"
                Leaf.BottomSurface = "Smooth"
                Leaf:MakeJoints()
                Val = Val +1
                if Val == 10 then
                    Val = nil
                    VectorX,VectorZ = nil
                    break
                end
            end
        end
        holderFrame.Generate.Text = "Generate"
        game.Workspace.Camera.CameraType = "Fixed"
        InProgress = false
    end
end