I cannot unblock enrollment in my itunes u course

When I have my students try to enroll in my course using the course number, it gives them a message that they cannot enroll and to contact their instructor. When I log in to the course under admin and try to turn off the block enrollment it turns green and then immediately turns back to blocking. I get a message that says: Unable to save changes. Another instructor modified this course while you were making changes. To try again, cancel your edits and start over from your Library.

I don't know what to do. I have not signed into another account or device. Any ideas?