caspar20:
Welcome to the Apple Discussions. Was the problem photo edited with Photoshop Elements or Photoshop? Is it from the same source as the other files in it's roll?
You might try the following:
1 - download the "Embed sRGB Profile" Automator application from
Toad's Cellar.
2 - locate in the Finder the folder that contains the original problem files.
3 - select the problem files or all the files in that folder and drop onto the application that you downloaded.
4 - launch iPhoto and try again.
iPhoto has issues with files that do not have a color profile embedded in them or damaged profiles. This is a quick way to determine if those are of that nature.
Do you Twango?
TIP:
For insurance against the iPhoto database corruption that many users have experienced I recommend making a backup copy of the Library6.iPhoto database file and keep it current. If problems crop up where iPhoto suddenly can't see any photos or thinks there are no photos in the library, replacing the working Library6.iPhoto file with the backup will often get the library back. By keeping it current I mean backup after each import and/or any serious editing or work on books, slideshows, calendars, cards, etc. That insures that if a problem pops up and you do need to replace the database file, you'll retain all those efforts. It doesn't take long to make the backup and it's good insurance.
I've written an Automator workflow application (requires Tiger), iPhoto dB file backup, that will copy the selected Library6.iPhoto file from your iPhoto Library folder to the Pictures folder, replacing any previous version of it. You can download it at Toad's Cellar. Be sure to read the Read Me pdf file.