Susan, et. al.
I have a suggestion I'd like you to try....
I'm assuming you are using a large image folder on your desktop (100+ images, maybe thousands) and you are selecting that folder on the Auctiva Uploader and then adding the images from the upper box to the lower box as your group to upload.
Instead of using that large folder, here's my suggestion. Create a new folder and move only 20 to 30 images to the folder. Select that folder in the uploader, but wait to do the add until all of the images display as thumbs in the upper box. Note, this is allowing time for the uploader to pre-process the images.
Try that and please post back your result.
Danno