On some of my pages, The RIE gives an error, "Undefined property" (see e.g. http://ehinger.nu/undervisning/index.php/starta-haer/nyheter/5535-kaskeloter-i-sodra-stilla-havet.html
under "Läs också..." and "Också intressant"). It seems the error appears when the first link in the linked related article is to a Youtube video, or when there aren't enough related articles to link to.
What might be the cause of this error?