When importing an iPhoto Library, it's possible to get an alert message that says "Inaccessible iPhoto Images."
This happens if you import images from a folder that contains an albumdata.xml file, which normally resides in your iPhoto Library folder. Images normally do not reside in this folder, because iPhoto puts them in subfolders within the iPhoto Library. Thus this issue should only occur if you have either rearranged images manually or copied the albumdata.xml into a folder containing images.
You should not manually move, rename, or delete any images or files in your iPhoto Library folder.
Please update to the latest software version if you continue to experience this issue.
Choose Apple > Software Update to make sure you have the most recent upgrade.
This issue is resolved in Aperture 1.5.