Hello Larry -
eBay's API will provide such notifications when there is a product in their catalog which should be associated with your listings. If there is a match in the product catalog, eBay would prefer that you include those specific details in your listings.
When you are creating a listing in Auctiva, after you have added your category there will be a link available to check the product catalog - this link is just beneath the Item Condition Note on the lister page and is the words: "Find Product".
Including these details in your listings should clear up the API warnings.
If you are also experiencing issues with API failure notifications and need assistance with those listings, please file a support case from under the Help tab of the site and leave the notifications intact in your account. Please include the titles of a few examples where such has occurred for you and we'll be happy to assist you further.
- Craig