TRIAL & ERROR
Have they got the same file extension eg *.jpg?
If they have delete say 75% of the files - you say you have a back of them all anyway. Then try opening up the folder/file. If this does not work delete all the files except one and see what happens. If you still have a prob delete the folder and create it again and see what happens by loading a few *.jpg, if OK load them all back in. David