[basvanderwerff]

Putting in

frame:SetScript("OnEvent", function(self, event, ...)
    if ... == addonName then
        BetterItemTooltip:OnInitialize()
    end
end)
frame:RegisterEvent("ADDON_LOADED")

did the trick no errors or anything after that i ran

/run SetCVar("breakUpLargeNumbers", 1)

Now the addon works and it wont mess with large numbers anymore.

Thanks alot for those that helped to get it working good.