Thumbnails and full image will not display in iPhoto

I have recently migrated my data from a 20 inch iMac to a 27 inch iMac both of which were fully up to date. Since doing the migration, I have erased and sold the 20 inch iMac and now upon closer inspection of the new mac, I have discovered that some of my events in iPhoto (mostly photos added from Sept-now) are not working properly.

To look at the events they appear fine when opening iPhoto for the first time after turning the mac on. The image is there that represents the event, you click on it, all the images are there with their thumbnails but when you click on it, there's no image but just a grey canvas with an exclamation mark in a triangle in the centre of where the image should be. When you click to go back to view the rest of the images, all the thumbnails are grey and when looking at the events the representing image has also gone. Some events haven't even shown me any thumbnails other than the grey error image.

I have tried running all the repair options available that appear when pressing command and option when opening iPhoto and no joy! Also tried making a new library and importing the iPhoto library file from an old time machine backup but still no joy.

Im sure the images are there somewhere because of the brief preview you get when you open iPhoto for the first time and also when I scroll through my events, all the representing images show but when I stop scrolling they go back to a grey empty box.

Please help!