"Image cannot be loaded. Make sure…"

Users can see the list but when they click this message appears:”Image cannot be loaded. Make sure the path is correct and the image exist”

Ok…. But the image exist and the path is correct.
Something else has to be happening.
Any idea?
Thanks

http://wordpress.org/plugins/user-files/