eBay will return this error when it detected that the product description’s contains active content (eg Javascript) within its HTML code (inside your eBay template).
Note that active content had been totally forbidden by Ebay since the beginning of June 2017.

Check the contents of the descriptions (both in Prestashop and in your template), if you are using javascript, remove all the active scripts and retry the sync.
Do not use {GALLERY_V} placeholder to generate the dynamic pictures gallery within the description in a non-upgraded module version (before v5.4.6) since it containts active content.

In the latest versions of the module, you can send multiple product and variation pictures directly inside the eBay picture gallery and include static pictures of your products using placeholders for individual images.
We remind you that our agency module shop offers advanced Fastbay templates fully compatible with Fastbay and new eBay 2017 rules.
For more information or details about eBay specifications regarding active content, check out this link:  https://pages.ebay.com/sell/itemdescription/bestpractices.html