IPhoto 9.6 - Library will not upgrade...

Question

MacBook Pro (15-inch, Mid 2010), 2.4 GHz Intel Core i5, 8 GB 1067 MHz DDR3, Intel HD Graphics 288 MB.
OS X Yosemite, Version 10.10.
iPhoto 9.6
Library size - 48GB
PROBLEM.
I upgraded iPhoto and everything worked great. However a few days ago when opening the App a message appeared telling me my library needed to be upgraded to use this version of iPhoto.
I have selected upgrade on several occasions but all that happens is the "Beachball" for approximately 10mins and then the App closes, occasionally it will get as far as "examining photo library" but still shuts down.
ATTEMPTS TO CURE
1.     I have tried holding down the Cmd + Opt keys on selection of the App and have selected every option on the iPhoto First Aid but it will not allow me to do anything other than "Upgrade" or "Quit"
2.     I have opened the App holding down the Opt key and created a new library - iPhoto then works fine. However when I try to change libraries I'm back where I started.
3.     I have removed and reinstalled iPhoto (ensuring my library was backed-up first) - no change.
4.     I have downloaded iPhoto Library Manager. It finds my library and my albums but none of my pictures - is this because I need to pay the £20?
Any help would be gratefully received.

Answer 1

If rebuilding your library with iPLM doesn't work or fails to recover your photos you may have to resort to the following;
Starting over from scratch with new library
Start over with a new library and import the Originals (iPhoto 09 and earlier) or the Masters (iPhoto 11) folder from your original library as follows:
1. Open the library package like this.
2. Launch iPhoto with the Option key held down and, when asked, select the option to create a new library.
3. Drag the subfolders of the Originals (iPhoto 09 and earlier) or the Masters (iPhoto 11) folder from the open iPhoto Library package into the open iPhoto window a few at a time.
This will create a new library with the same Events (but not necessarily the same Event names) as the original library but will not keep the metadata, albums, books slideshows and other projects.
Note:  your current library will be left untouched for further attempts at a fix if so desired.