AddEventHandler("iblock", "OnAfterIBlockElementUpdate", "PS_LogElementUpdate");
AddEventHandler("iblock", "OnAfterIBlockElementAdd", "PS_LogElementAdd");

function PS_LogElementUpdate(&$arFields)
{
    global $USER, $DB;

    if(!$arFields["ID"]) return;

    $userId = is_object($USER) ? intval($USER->GetID()) : 0;
    $elementId = intval($arFields["ID"]);

    $DB->Query("
        INSERT INTO b_event_log
        (SEVERITY, AUDIT_TYPE_ID, MODULE_ID, ITEM_ID, USER_ID, DESCRIPTION)
        VALUES
        ('INFO','UPDATE','iblock','{$elementId}','{$userId}','Изменён товар ID={$elementId}')
    ");
}

function PS_LogElementAdd(&$arFields)
{
    global $USER, $DB;

    $userId = is_object($USER) ? intval($USER->GetID()) : 0;
    $elementId = intval($arFields["ID"]);

    $DB->Query("
        INSERT INTO b_event_log
        (SEVERITY, AUDIT_TYPE_ID, MODULE_ID, ITEM_ID, USER_ID, DESCRIPTION)
        VALUES
        ('INFO','ADD','iblock','{$elementId}','{$userId}','Добавлен товар ID={$elementId}')
    ");
}<pre>[Error] 
Call to a member function CanDoOperation() on null (0)
/home/s/sizenkjh/magicroom.store/public_html/bitrix/modules/main/include/epilog_after.php:22
#0: require
	/home/s/sizenkjh/magicroom.store/public_html/bitrix/modules/main/include/epilog.php:3
#1: require_once(string)
	/home/s/sizenkjh/magicroom.store/public_html/bitrix/footer.php:4
#2: require(string)
	/home/s/sizenkjh/magicroom.store/public_html/bitrix/php_interface/init.php:38
#3: include_once(string)
	/home/s/sizenkjh/magicroom.store/public_html/bitrix/modules/main/include.php:115
#4: require_once(string)
	/home/s/sizenkjh/magicroom.store/public_html/bitrix/modules/main/include/prolog_before.php:14
#5: require_once(string)
	/home/s/sizenkjh/magicroom.store/public_html/bitrix/modules/main/include/prolog.php:10
#6: require_once(string)
	/home/s/sizenkjh/magicroom.store/public_html/bitrix/header.php:1
#7: require(string)
	/home/s/sizenkjh/magicroom.store/public_html/catalog/index.php:1
----------
</pre>