I'm getting this error when entering the catalog page. The view to enter new products is empty at least it doesn't have form inputs. Looking through same reports on google and this forum I came to a lot of settings to change but none of them helped.
The permissions on var/cache were even tested with chmod 777.
I'm trying to figure out the root cause. The sys log only shows
2016-05-03 12:03:28] main.CRITICAL: Block product_tabs throws exception and cannot be rendered.   [2016-05-03 12:03:28] main.CRITICAL: Could not determine temp directory, please specify a cache_dir manually  
But the debug.log has no entry.
I don't even know which of these caches the error message refers to.
Just for testing I set everything to 777 so I'm now 100% sure it's not related to permissions.