Просто выберите данные, не обращаясь к Activation_status, и проверьте их с помощью оператора if.
EDIT:
Код, который вы, вероятно, ищете:
$LoginRS__query=sprintf("SELECT user_handle, user_password, activation_status FROM users_entity WHERE user_handle=%s AND user_password=%s",
GetSQLValueString($loginUsername, "text"), GetSQLValueString($password, "text"));
$LoginRS = mysql_query($LoginRS__query, $f12_database_connect) or die(mysql_error());
$loginFoundUser = mysql_num_rows($LoginRS);
if ($loginFoundUser) {
// Make sure user is activated.
$row = mysql_fetch_Array($LoginRS);
if ($row['activation_status'] === 'Pending') {
header("Location: some-other-page");
}
$loginStrGroup = "";
//declare two session variables and assign them
$_SESSION['MM_Username'] = $loginUsername;
$_SESSION['logged_in']="True";
$_SESSION['MM_UserGroup'] = $loginStrGroup;
if (isset($_SESSION['PrevUrl']) && true) {
$MM_redirectLoginSuccess = $_SESSION['PrevUrl'];
}
header("Location: " . $MM_redirectLoginSuccess );
}
else {
header("Location: ". $MM_redirectLoginFailed );
}
}