if ($2 && $readini(ban.ini,$2) == $null) {
      writeini ban.ini $2
      echo -a User has been added to the ban list.
      if ($readini(ban.ini,$2) != $null) echo -a This person is already on your ban list.
    }

The bracket should go before the second if:

    if ($2 && $readini(ban.ini,$2) == $null) {
      writeini ban.ini $2
      echo -a User has been added to the ban list.
    }
    if ($readini(ban.ini,$2) != $null) echo -a This person is already on your ban list.