Images not showing on image uploader

I know this problem was solved in other threads, but mine is a little different.

1. I (the admin) can make uploads and see images on media uploader and select them for post normally.

2. The author of the posts can upload but can’t see the images to select them for the post.

3. He was able to do this some weeks ago.

4. I checked with him and saw for myself that the problem was real.

Any ideas? thanks