Hi Jean,
Now that I've seen your store and listings (other Forum thread), I hope I can help.
I think you probably mean the "Gallery" image, which is a Thumbnail picture that appears in the listing gallery during search or in your Store. That image is the same as the "Header" image on a listing (just smaller). Both of those images are hosted by ebay (now), so a change/upate to the Auctiva image in your Auctiva image library probably won't fix those (at least not immediately). To get them both fixed, I'd use the ebay Revise listing and reload/refresh the pictures.
There is also a new method to refresh/change just the Gallery image. Click on "Site Map" at top right on any ebay page and locate "Change Your Item's Gallery Image" in center column under Sell heading. You'll need the listing number to use that method. Note, you don't need to change and can use that with the existing URL link to the Auctiva image to simply refresh (that reloads an updated image from Auctiva's server to ebay).
Danno