I'm receiving this error message periodically:
Photos for the iCloud account "firstname.lastname@example.org" cannot be accessed. Review your account information in System Preferences.
Photo Stream is enabled on my iPhone, and the Photo Stream in iPhoto 9.4.2 is updating absolutely fine. iCloud in System Preferences allows me to manage backups, buy more storage and change Photo Stream options with no errors.
This feels like an OS X bug?