Ok the problem was, For a receiver to grant permission to refund to the API Caller:
Login to www.paypal.com (For Sandbox: www.sandbox.paypal.com - Make sure you are already signed in https://developer.paypal.com) and login with the receiver account. Goto Profile -> API Access -> Grant API Permission -> Input the API Caller (Example: May6_1307031077_biz_api1.paypal.com) in Third Party Permission Username textbos and click Lookup button -> Enable checkbox for "Issue a refund for a specific transaction" and click Add button.
This is how receiver can grant permission to API Caller.
Once this is enabled, the refund should work.
Founded in https://www.x.com/developers/paypal/forums/adaptive-payments-api/adaptive-refund-notprocessed
Edited.......
You can see on https://www.x.com/devzone/articles/paypal-permissions-and-advantages-integrating-permissions-api If you need make this feature with Api you can use this gem:
https://github.com/moshbit/paypal_permissions
Thank you very much!