FocusFrame does not exist in Classic_Era, so have to check if it exists. Otherwise it bricks other things on init, like Target of Target, Party Frame, Raid Frame.
in hideblizzard.lua changing the focus function works.
focus = function()
if FocusFrame then
FocusFrame:UnregisterAllEvents()
FocusFrame:Hide()
end
end,

issue has been resolved in version 3.6