Originally reported/described here: http://moodle.org/mod/forum/discuss.php?d=140122
Create a course in a course category (e.g., "algebra1" within "math courses"). In that course, upload an image or other file to the "course files" area, and create a question that links to that file. Now try to move that question from the course to its parent category level (so that it can be shared by other courses in the category). When prompted what to do about the image, select either "copy from the course files area and change links" or "move from the course files area and change links." The result is the error message seen in the attached screenshot.
You may contact me directly for further info if needed: email@example.com