OK, I'm trying SU file manager and it shows a lock symbol next to the system folder, so I'm guessing that means I can't transfer to it. Yet I was able to delete from it yesterday with Android Mate but not transfer to it. Still at a bit of a loss here. Sorry.
Edit - if it helps I rooted using RyanVA's oclf.
Edit again - problem solved. Just gotta find the right app. Root explorer did it for me.