Iphoto shows loading photos for a book, but loading does not complete

Hi all, I'm hoping someone can help me. I have put together 5 books in Iphoto, and today selected about 60 photos to create a new book. I selected the photos and clicked on "add to" at the bottom of the screen. I then selected "book" and from there "create book". The screen then transfers to "Loading" and the "little progress wheel" appears. The wheel then stops and Iphoto does not progress any further. I then need to force quit to get out of iPhotos. Does anyone out there know what the problem is and how I can fix it?

Thanks, Marcus