I kept receiving the same eBay.de API error that the original poster described- indicating that I was using videos or javaScript in my listing although I was not- and it was driving me mad! After hours of trial and error, I'm happy to say that I FINALLY figured it out and I'd like to share what worked for me...
Go to My Account > Account Preferences > Listing Enhancements. Make sure all the Auctiva add-ons are turned OFF. That includes the Scrolling Gallery, BuyShield Warranty Widget, Battlebids, and Sellathon Counter. I think the BuyShield Warranty Widget was the main problem, but just to be safe I turned off all the listing enhancements.
I guess eBay.de does not support Auctiva's ads?
Anyway, I hope this solution helps!