Sorry, I should have been clearer! I'm doing it on the website, as usual, and have the permissions needed. The courses weren't in play either.
Looking back, I had this problem a couple of weeks or so ago - about editing an existing course - although creating a new one seems fine.
But I wouldn't like to keep recreating courses from scratch in order to edit them!
I've never had this issue before until that first problem emerged (in May probably).