This error means that ebay can't obtain an image for your product to put it on ebay.
There few possibility why this may happen.
1) Hotlink protection in hosting
2) Image for select type does not exist (you will need to regenerate thumbnails)
3) Connection issue

To understand better what is the issue you can send an only single image for the product to ebay. This can be done in Selling Profile. You will need to set "No Gallery". And if you have active send image for variation, deactivate it. After that try to list item. After you get "Success" message open item on ebay and check image for it. 

Usable PrestaBay module to re-generate images is