I suspect this is another issue related to MDL-11347 which only seems to be occuring on an upgrade. But I'll create the issue so I remember to check it.

I've upgraded a site which has a complicated course category layout, simplified:

• X
  • • Y [hidden]
      • • • Z [hidden]

I am an admin,

I can browse to sub cat fine, but when I try and browse to sub sub cat I get 'That is not currently available' at line 47 of course/category.php: call to error().

Which means as an admin i'm failing to receive has_capability('moodle/course:create', $context) at that category context

(To make it more hazy there are some roles assigned at context Z!!)