[Luis-]

pawn Code:

CMD:admins(playerid) {
    new string[128+MAX_PLAYER_NAME], plName[MAX_PLAYER_NAME];
    foreach(Player, i) {
        if(PlayerInfo[i][pAdmin] != 0) {
            GetPlayerName(i, plName, sizeof plName);
            format(string, sizeof string, "%sAdmin: %s(%d)\n", string, plName, i);
        }
        ShowPlayerDialog(playerid, DIALOG_ID, DIALOG_STYLE_MSGBOX, "Admins Online", string, "Okay, "");
    }
    return 1;   
}

Should work.