предположу что там SECTION_CODE или SECTION_CODE_PATH и у раздела не указан символьный код
$arSelect = Array(
'ID',
'DETAIL_PAGE_URL'
);
$arFilter = Array(
'IBLOCK_ID'=> $arResult['IBLOCK_ID'],
'ID' => $arResult['ELEMENTS']
);
$db_res = CIBlockElement::GetList(Array(), $arFilter, false, false, $arSelect);
while($arElement = $db_res->GetNext()) {
$refURL[$arElement['ID']] = $arElement['DETAIL_PAGE_URL'];
}
foreach ($arResult['ITEMS'] as $k=>$dctItem) {
$arResult['ITEMS'][$k]['REAL_PAGE_URL'] = $refURL[$dctItem['ID']];
}