WoWInterface - GetName Error

Hi! How to do a background check so as not to give an error when using :GetName() in the Game Shop or Send Twitter
My Lua code:

Lua Code:

local SFN = CreateFrame("Frame")
SFN:SetScript("OnUpdate", function()
    local f = GetMouseFocus()
    if f then
        local n = f:GetName() or tostring(f)
        if n then
            FramerateLabel:SetText(n.." - FPS: ")
        end
    end
end)

Error:

Code:

Message: Interface\AddOns\WorldTools\Libs\lib_hook.lua:29: Attempt to access forbidden object from code tainted by an AddOn

Time: 04/22/15 04:48:51

Count: 182

Stack: [C]: in function `GetName'

Interface\AddOns\WorldTools\Libs\lib_hook.lua:29: in function <Interface\AddOns\WorldTools\Libs\lib_hook.lua:26>



Locals: (*temporary) = <unnamed> {

 SplashBanner = <unnamed> {

 }

 CurrentMarketPrice = <unnamed> {

 }

 NormalPrice = <unnamed> {

 }

 InvisibleMouseOverFrame = <unnamed> {

 }

 Strikethrough = <unnamed> {

 }

 GlowPulse = <unnamed> {

 }

 IconBorder = <unnamed> {

 }

 SplashBannerText = <unnamed> {

 }

 Icon = <unnamed> {

 }

 UpgradeArrow = <unnamed> {

 }

 Shadows = <unnamed> {

 }

 BuyButton = <unnamed> {

 }

 ProductName = <unnamed> {

 }

 Checkmark = <unnamed> {

 }

 Magnifier = <unnamed> {

 }

 Model = <unnamed> {

 }

 BannerFadeIn = <unnamed> {

 }

 0 = <userdata>

 Card = <unnamed> {

 }

 GlowSpin = <unnamed> {

 }

 Description = <unnamed> {

 }

 CurrentPrice = <unnamed> {

 }

 SalePrice = <unnamed> {

 }

}