The support of IJoomla (excellent BTW) helped me out a while ago.
Don't understand fully, but this is what they did:
In components/com_sef/joomsef.php file is a function called "getMenuTitle"
where Artio sef make a select in database to find section title from menu.
"SELECT name$jfTranslate FROM #__menu WHERE link = 'index.php?option=$option'"
This select don’t verify after "published=1" and if exist in table #__menu, old registration with the same name, code do some trouble even they are unpublished or deleted.
In your case (
www.medischondernemen.n) there were 2 more registrations in table which were deleted/unpublished but code crashed.
I modified field “link” from "index.php?option=com_news_portal" in "index.php?option=com_news_portal2" and works.