Rudy,
I had a similar problem this evening. When I discovered the missing picture, here's what I did:
1. list another item, with only the bare minimum data;
2. upload the missing picture to this 'reload' listing;
3. assuming the picture uploads OK, make a note of the new (reload) listing number;
4. go back and edit the listing that was missing it's picture. In the "edit" page you can enter a URL for the missing picture. The format is: http://www.choochooauctions.com/tcimages/69xxx_1.jpg (the 69xxx represents your SECOND listing number with the picture);
5. save the change to the original listing;
6. take another look at the problem listing. If everything has worked, the picture should be there.
7. return to the 'upload only' listing and END IT EARLY. DO NOT DELETE IT!!! (I did, and the picture was gone again );
That should do it! I know it's a pain...but it works.