I found this problem when I upgraded. When you go into Pictures, there's an iPhoto icon that says 'iPhoto Library'. To get the actual pictures, you have to right-click the icon and select "Show Package Contents". It's always best to make a copy just in case. Anyway, this will bring up a new finder window with folders and a couple of icons. The only 2 folders you should worry about are Modified & Originals.
Hope this helps. 🙂