The problem is this: On the start page, various HikaShop modules (HikaShop Content Modules) are integrated, which refer to different products in the catalog. If you click on one of these products you get the following error message:
Fatal error: require_once(): Failed opening required '/homepages/3/d205006342/htdocs/bfk2014/libraries/joomla/document/html/renderer/head.php' (include_path='.:/usr/lib/php7.2') in /homepages/3/d205006342/htdocs/bfk2014/templates/rt_plethora/error.php on line 134
This is not nice at all, especially since the same module works without problems at another location. As an example I take the module on the start page "Unsere Gebrauchten - Immer einen Blick wert" (at the bottom of the page). If I click on one of the products there, I get the above error. I integrated the same module here as well:
(also scroll down here). If I click on one of the products here, everything works fine.
I would be incredibly grateful if you could give me a hint on how to fix this problem.