Google Announcement Today:

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.

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 remove all referral code from your sites before the last week of August, so you can continue to effectively monetize your ad space.

Google Inside AdSense Team