I have an instructor who is grading a forum by rating students' posts. (Only the instructor has permission to rate.) It was set to a maximum grade of 10, but she wanted it changed to a maximum grade of 6. She requested this change after she'd already rated students. Now, when I try to change the maximum grade, I get the error(s) shown in the attachment. They seem to contradict one another: one says I can't change the maximum grade, and the other says I can change the maximum grade after rescaling. I don't even see anywhere to rescale the grades. How can I change the maximum grade for this forum?
You're right - the messages do indeed contradict one another. Unfortunately, it seems it's a bug in Moodle 3.1 and 3.2 - see MDL-56949. Please vote for the issue to indicate that you'd like it to be fixed. (You'll need to create a tracker account in order to vote.)