[LocMax]

The content of the dialog is too long.
You need to reduce number of \n's and number of letters/messages, keep only the needed stuff.

pawn Код:

CMD:rules(playerid, params[])
{
    ShowPlayerDialog(playerid, DIALOG_RULESCMD, DIALOG_STYLE_MSGBOX, "GenerationGamers Rules", "Do not beg to become an admin.\nDo not advertise.\nDo not ask for VIP.\nDo not insult/provoke.\nDo not spam or flood.\nBreaking these rules will result in a ban.\n\nhave fun!", "Accept", "Decline");
    return 1;
}