As of this morning, when I try to open iPhoto I get the following message: "The photo library needs to be upgraded to work with this version of iPhoto." Beneath which reads: "Your photo library will not be readable by previous versions of iPhoto after the upgrade. The upgrade process for very large libraries may take an hour or more to complete." This has never happened before. I upgraded from '09 to '11 last year as soon as it became available, but have never encountered this until today. I am, at this point, unwilling to click on the Upgrade button. Advice appreciated. Thanks.