$db_props = CIBlockElement::GetProperty($PRODUCT_IBLOCK_ID, $PRODUCT_ID, "sort", "asc", Array("CODE"=>"FORUM_TOPIC_ID"));
<? $db_props = CIBlockElement::GetProperty($PRODUCT_IBLOCK_ID, $PRODUCT_ID, "sort", "asc", Array("CODE"=>"FORUM_TOPIC_ID";)); ?>