after iPhoto upgrade i can no longer access the photos stored on my external hard drive, after iPhoto upgrade i can no longer access the photos stored on my external hard drive

I was just about to order a photo book, using photos stored on an external hard drive. I organised the book and pressed 'buy'. IPhotos instructed me that I needed to upgrade and so I went on the ASpp store, bought the upgrade and installed as directed. I then used the iPhoto Library upgrader as directed.

After the iPhoto upgrade I can no longer access the photos stored on my external hard drive. I am able to access the photos stored on my internal hard drive - the remainder (including the photo album) seem to have vanished into thin air.

Any suggestions please?