When you're in edit mode on your page, click the link under the picture to remove it. Then click to add a picture, and you should be able to pick any picture from your gallery. Can you try that? I just did it on my page and it worked fine.
"You may have a fresh start any moment you choose, for this thing that we call "failure" is not the falling down but the staying down." Mary Pickford
"No matter how slow you go, you are still lapping everybody on the couch."