What is behind the idea that some pages work while others don't (in admin)?
That is on a clean install without any, Zero, alterations done yet.
E.g.: Design>Theme & Logo, or:
Catalog>Categories, Catalog>Attributes & Features, etc.
While other pages under the same item work, like e.g.: Catalog>Products, etc.
Albeit, and given the above said, it doesn't make sense anyway that this should have to do with file permissions, I went ahead and checked file permissions manually but gave up after 10 minutes, realising I could be on there for the next two days, considering the number of folders/files. I still used the terminal command to set files to 644 and folders to 755 (one never knows what craziness is hidden in the code) but it's still the same. I either get a internal server error or a 500 error page. Something with a missing token. Right?!