Problems with "Save Changes" or "Post" in iPad as well as in iTunes U Course Manager (Safari)

It shows "Unable to Save Changes"

Message with the content:

"Another instructor modified this course while you were making changes. To try again, cancel your edits and start over from your Library"

By the way, I use this course alone so no one can modified my course and at that time I already use just one device for iTunes U course . It happens several times. However, during I get the message "Unable to save change...I notice that my students can see my post already.