In a recent announcement Amazon informed that they will be changing some affiliate links. As of July 31 2015, the old links will STOP working if they are not replaced with the new ones. The change is as follows:
1. ws.amazon.com should be replaced with ws-na.amazon-adsystem.com
2. rcm.amazon.com should be replaced with rcm-na.amazon-adsystem.com
If you added your amazon links recently you probably won't find any links on your blog using the old format that will cease to work. But, if you have old links you should replace them. Not only you won't get any commission for the sales referred to Amazon, but you will send your visitors to broken links.
If you are a happy Auto Affiliate Links user, this update won't affect you because all the links are frequently regenerated. If you added your links manually trough your blog posts, then you might have a lot of work to do to replace all links. A fast way is to search your database for the old url and automatically replace it with the new one, but this will require some programming knowledge.