EXPORT ERROR

Hi,

When I go to export few different photos, sometimes one of them exports as a duplicate image of one the other photos, and it over rides what the actual image should be. 

Example - Export image 1,2 and 3. The image 3 exports as the image 2 and becomes a duplicate. Image 3 no longer exists, even though the file name remains how it should be. Any thoughts? I would really appreciate any suggestions on how to fix it!