ESOUI - AnchorFill error upon initial group creation...

I am currently working on updating WarLegend Group Frames to current API, etc. for re-release once I get hold of Lyeos...
So far I have managed to iron out everything to working order, with a helping hand on a couple of minor issues (Thank you again Garkin & Minceraft!)

I'm completely stumped on this one issue that I just can't get around... Every initial group creation per session the anchorfill for the background throws an error, once a reloadui is done, all is fine and working perfectly until next session or relog.

Here is the code if someone has any ideas as to how to resolve this one last issue:

Warning: Spoiler

Code:

local function WLGF_ManageControl(num)

        local ctrl  = "ZO_GroupUnitFramegroup"

        local frame  = _G[ctrl..num]

        local name  = _G[ctrl..num.."Name"]

        local hp_bar = _G[ctrl..num.."Hp"]

        local bg          = _G[ctrl..num.."Background"]

        local Ucount = 0

        local owner  = "group"..num



        local edge_tex          = "EsoUI/Art/Tooltips/UI-Border.dds"

        local center_tex = "EsoUI/Art/Tooltips/UI-TooltipCenter.dds"



        if (WLGF["Anchor_group"..num] == nil) then

                WLGF["Anchor_group"..num] = Chain(WINDOW_MANAGER:CreateTopLevelWindow("WLGF_Anchor_group"..num))

                        :SetDimensions(WLGF_SAVE.MW_width - 30, WLGF_SAVE.Bars_H + 25)

                        :SetMouseEnabled(true)

                        :SetHandler("OnMouseUp", function(self, button) WLGF_RightClick_Click(button, owner) end)

                .__END



                WLGF["Anchor_BG"..num] = Chain(WINDOW_MANAGER:CreateControl("WLGF_Anchor_BG"..num, hp_bar, CT_BACKDROP))

                        :SetAnchorFill(WLGF["Anchor_group"..num])

                        :SetCenterColor(1,1,1,0.5)

                        :SetHidden (true)

                .__END



                WLGF["HP_Text_group"..num] = Chain(WINDOW_MANAGER:CreateControl("WLGF_HP_Text_group"..num, hp_bar, CT_LABEL ))

                        :SetFont("WarLegendGroupFrame/fonts/"..WLGF_SAVE.HPT_font..".ttf|"..WLGF_SAVE.HPT_size.."|soft-shadow-thick")

                        :SetDrawLayer(4)

                        :SetColor(WLGF_SAVE.TC[1],WLGF_SAVE.TC[2],WLGF_SAVE.TC[3])

                        :SetAnchor(RIGHT, hp_bar, RIGHT, -25,0)

                .__END



                WLGF["HP_Perc_group"..num] = Chain(WINDOW_MANAGER:CreateControl("WLGF_HP_Perc_group"..num, hp_bar, CT_LABEL ))

                        :SetFont("WarLegendGroupFrame/fonts/"..WLGF_SAVE.HPP_font..".ttf|"..WLGF_SAVE.HPP_size.."|soft-shadow-thick")

                        :SetDrawLayer(4)

                        :SetColor(WLGF_SAVE.PC[1],WLGF_SAVE.PC[2],WLGF_SAVE.PC[3])

                        :SetAnchor(LEFT, hp_bar, RIGHT, 10,0)

                .__END

Many thanks in advance if someone can throw some ideas/suggestions which lead to squashing this one last issue.