If you get this error, it means that the Amazon API “thinks” that you are sending too many requests to it in too short a time.
You can use the ASA2 cronjob to avoid this. It can also be used without server-side configuration using the WP Cron API. For more details check out the cronjob manual.
Just as likely is that the frequency of your requests is wrongly calculated by the Amazon PA API. For many users who receive this message, it also occurs via the Amazon Scratchpad, which is a test environment of Amazon itself.
According to user reports, a reference to this fact with the scratchpad helped that the Amazon support had taken care of the matter. Otherwise, the Amazon support always sees the reason for the problem in the user’s application.
You can contact Amazon support by logging in to the PartnerNet homepage and clicking “Contact” in the “Help” menu. Here you can find a list of all Amazon PartnerNet sites.