I know 5 of my friends that have had active google adsense accounts with ads showing and all. But when tried to sign up to Google Affiliate Network, they got a message saying they're not allowed to sign up.
Curiously, those whose adsense account is NOT active (not getting second approval) can sign up to GAN. Indonesians are affected. My philipine friends don't. Also only new accounts made in last 3 months have this issue I think.