I saw your test post, Chuck. The site works fine if someone uploads a small enough image. I created another ad, so you can see what happens if someone tries to upload a 2.6MB image. We can't expect every user to know not to try to upload a huge file.
So if you login again as admin, and click to edit my new test ad you can see what's happening per the screenshot above. It's spreading the name of that one huge file out over the whole list of thumbnails... one letter for each thumbnail. Then the ad becomes corrupted and you can only upload one photo, no more.