I viewed your post and i got it to work. I found that the Developer Portal instructions (deleting, clean, delete, restart and resetting the profile) worked for me. I also pinned down that adding the iTunesArtwork file in the already build .App package does lead to the same error.
So i added it into Xcode (on root level of project) and compiled the WHOLE package with signing. That DOES work.
Thanks for your assistance!
I uploaded my ap on the 7th of januari so i hope it will be ready for sale soon...
(More info on:
EeKay Online » EeKay Online)