I'm getting bit by this bug weekly it seems. You can self-reference an article. So if you have a type Product and you have an Article (Related) field pointing to a category containing Product content types, you can self-reference the exact article you're in with itself.
My solution is to make it is to add a check against the current article ID in the database query on line 200 of plugins/cck_field/joomla_article/joomla_article.php:
$opts2 = JCckDatabase::loadObjectList( 'SELECT title AS text, id AS value FROM '.self::$table.' WHERE catid IN('.$options.') AND state = 1 ORDER BY title', 'value' );
I did not modify the line above, but I would add in AND value != '.$article->id.' (whatever is the id of the current article)
When articles can self-reference, you get infinite loops and out of memory errors.