From Adsense Blog :
We’re constantly looking for ways to improve AdSense by developing and supporting features which drive the best monetization results for our publishers. Sometimes, this requires retiring existing features so we can focus our efforts on the ones that will be most effective in the long term. For this reason, we will be retiring the AdSense Referrals program during the last week of August. We appreciate your patience during this transition and here are some alternative options to consider:
* Google Affiliate Network: As part of the integration of DoubleClick, the DoubleClick Performics Affiliate Network will now operate as the Google Affiliate Network for advertisers targeting users located in the United States. Similar to the AdSense Referrals program, the Google Affiliate Network enables publishers to apply for advertiser programs and get paid based on advertiser-defined actions instead of clicks or impressions. For further details, please visit: http://www.google.com/ads/affiliatenetwork/.
* AdSense for content ads: If you have less than three AdSense for content ad units on a page, you may wish to replace the referral ad units with standard AdSense for content ad units.
If you currently use referral ads, either to promote Google products or offerings from AdWords advertisers, AdSense Referrals code will no longer display ads beginning the last week of August. We encourage you to take the following steps before the product is retired:
* Remove the referral code from your site(s): Please take a moment to remove all referral code from your sites before the last week of August, so you can continue to effectively monetize your ad space.
* Run and save all referrals reports on your desktop: Create and save all reports related to the referrals program on your desktop, so you continue to have access to your valuable campaign information.
Thank you for your support of AdSense Referrals in the past. If you have any additional questions, please visit our Help Center.