One or more of the photos you ordered is missing. When you look at the photo in the library, it has a ? character in its filename.
This happens when using:
Before you order prints, make sure none of the photos in your order have a ? character in their filenames. If any photo's name contains a ? character, rename it without using a ?. Follow these steps:
1. Select Photo Library.
2. Select the photo(s).
3. Choose Export from the File menu.
4. Click Export. Note: Take note as to where the photo(s) will be exported.
5. Rename the file without the ? character.
6. Choose Import from the File menu.
7. Select the photo(s).
8. Click Import.
Note: You will now have duplicate photos in the iPhoto Library. You might want to delete the photo with the ? character in the filename to prevent confusion when ordering prints.
Additional information
If a print order has a photo with a filename containing a ? character, the order will be set aside, and examined by Apple.
If the number of affected photos is less than 10 percent of the total order, the affected photos will be removed from the order. The billing statement will be updated to reflect that these photos were removal, and an email will be sent to you explaining the situation.
If the number of affected photos makes up more than 10 percent of the order, the whole order will be canceled, and an email will be sent to you explaining the situation.
You will not be billed for prints Apple can't process.