i had the same problem, so i did some edit
1. components/com_rss/rss.phpchange the line :
$query = "SELECT a.*, u.name AS author, u.usertype"
to this :
$query = "SELECT a.*, UNIX_TIMESTAMP(a.created) AS created_t, UNIX_TIMESTAMP(a.modified) AS modified_t, u.name AS author, u.usertype"
2. components/com_rss/rss.phpfind the
$item = new FeedItem(); and to the next lines :
// load individual item creator class
$item = new FeedItem();
// item info
$item->title = $item_title;
$item->link = $item_link;
$item->description = $item_description;
$item->source = $info[ 'link' ];
add the
$item->date line :
// load individual item creator class
$item = new FeedItem();
// item info
$item->date = ($row->modified_t > 0) ? $row->modified_t : $row->created_t;
$item->title = $item_title;
$item->link = $item_link;
$item->description = $item_description;
$item->source = $info[ 'link' ];
3. includes/feedcreator.class.phpchange the line :
$this->unix = 0;
to this :
$this->unix = $dateString;
Problem solved

(i don't write the line numbers cause i edited my elxis2006.4 with different line numbers. I think it will work in other version of elxis)
the results at
http://www.greekmasa.gr/cache/rss20.xml