[gmarco]

Uhm I have to rewritten it in this way:

if event == "PLAYER_LOGIN" then 
    local GMEXP_DEFAULTS = { LONGNRFMT = false, SCALE = 1, LIST = true, MAXLIST = 12 }
    for k in pairs(GMEXP_DEFAULTS) do
        if GMEXP_CFG[k] == nil then GMEXP_CFG[k] = GMEXP_DEFAULTS[k] end
    end
end

or the values = false are overwritten by defaults like they (I wrongly supposed) were nil. And it is not what I am looking for.
In this way it works.