https://affiliate-program.amazon.com/gp/advertising/api/detail/main.html

The changes, described below, will help us continue to provide you with relevant and useful features to advertise Amazon products. The following changes to the API will take effect on October 25, 2011:

Associate Tag will be a required and verified input parameter in all requests to the API
SellerLookup, SellerListingLookup and SellerListingSearch operations will no longer be supported by the API
ItemPage parameter will be limited to a maximum of 10 pages for ItemSearch results
MerchantId parameter will no longer be supported for filtering offers, variations and search results
Merchants search index will no longer be supported
Data returned by the Offers and ItemAttributes response groups will be limited to the most frequently used attributes