What exactly happens when you try to delete the pages? There are some pages that just cannot be removed, like the dust jacket and the fly leaves.
Also, you cannot delete a single empty page, if that would make the number of pages uneven. iPhoto will always delete multiples of two pages. So it is weird that your book has 61 pages. It looks like your book were corrupted in some way.
I'd duplicate the book and try, if the copy can be edited. First, I'd try to insert a single additional page just befor the last page, to make th number of pages even. Then try again to delete the last two pages.
If not, try to repair or rebuild the iPhoto library. See this post by Old Toad: Rebuild iPhoto Library, Version 11
Try the following:
1 - delete the iPhoto preference file, com.apple.iPhoto.plist, that resides in your
User/Home/Library/ Preferences folder.
2 - delete iPhoto's cache file, Cache.db, that is located in your
User/Home/Library/Caches/com.apple.iPhoto folder (Snow Leopard and Earlier).
or with Lion and Mt. Lion from the User/Library/Containers/com.apple.iPhoto/
3 - launch iPhoto, reset iPhoto's preferences and try again to delete the page.
NOTE 1: If you're moved your library from its default location in your Home/Pictures folder you will have to point iPhoto to its new location when you next open iPhoto by holding down the Option key when launching iPhoto. You'll also have to reset the iPhoto's various preferences.
NOTE 2: In Lion and Mountain Lion the Library folder is now invisible. To make it permanently visible enter the following in the Terminal application window: chflags nohidden ~/Library and hit the Enter button - 10.7: Un-hide the User Library folder.