In our Moodle 3.5.4 site, we can't change the category of our courses. I found discussion topics of about the same problem, MDL-63166 , in Moodle tracker site. However, I couldn't get an good information to solve it in the site. Fortunately, I got a good solution for it from Japanese Moodle community site. In order to solve it, adminstrator have to give the permission of couse:changecategory to authenticated user in the role override setting site of each category. I changed the permission for all of categories in our Moodle.