Currently Being ModeratedOct 7, 2013 5:17 AM (in response to melanieclover)
force quit iPhoto and restart the system.
If that does not fix the problem, rebuild your iPhoto library as described here by Old Toad:
Currently Being ModeratedOct 7, 2013 10:42 AM (in response to melanieclover)
Quit iPhoto and reopen it. Do you get the same message? If you do open your iPhoto library with the Finder as shown below
And look inside the Auto Import folder inside the library for any files that may be there. If there are any move them to the Desktop and restart iPhoto. Does that fix the problem?
If it does you can try to import those moved files again.