This can be caused by reasons such as:
- A bug in amazon API (not 100% the same as Amazon.com)
- temporary issue due to maintenance at Amazon.com
- too many search criteria (many keywords for example)
confuse the Amazon search engine.
The "remedy" (for now) is to use as few search criteria as possible.
- don't use keywords at all, and just use a category and subcategory
- start with 1 very "tight" keyword but without selecting a category or subcategory
If you want to use all your keywords, you can run the plugin more than once (maybe with a reduced scheduling frequency selected so you don't end up with 20 posts in one day).
Article ID: 2
Category: Associate Goliath Wordpress Plugin