There have been many changes in the Amazon affiliate program. One of the major changes is the tightening of access to the Amazon Prodiuct Advertising API. The news rules ...
1) New affiliates will not have any access until you have completed 3 sales and had a site inspection by Amazon.
2) Amazon Associates that have API access will have quotas enforced. This quota will be based on your sales volume and will be 0 if you have no sales in a 30 day period.
1) They are valid
2) They are not valid with a description of the problem
3) You have a quota restriction. This Amazon response will be "... you are submitting requests too quickly"