Hi,
Don't know if my suggestion would help but you could give it a try.
Auctiva recommend your pictures should be 1024 x 768 pixels for easier uploading to their image hosting site. I always resize my pics before I start the upload. The camera I use is an Olympus Camedia C70 and so far I have not encountered any problems with the uploads.
I also upload in bulk so that all my images are on the site ready to add to my listings.
Hope this helps.
Bye.