I-Photo & thumbnails...

Hi everyone

I have had my MBPr for about a week now and have opened up iPhoto quite a number of times but today, on launch, it said it 'needed to generate high resolution thumbnails' . This took a few minutes as I don't have a lot of pics in iPhoto.

Any idea as to why this only happened today and not on the first launch of iPhoto?

Thanks in advance

Charles