Remote radius serveur: one address address group external resource or internet service is required

hello guys,

i m using an external radius server, a fortigate 1000D, with FortiOS 6.2.

link & authentication between fortigate and radius server is OK.

But when i tried to use radius group on a policie, i have the error message below:

one address address group external resource or internet service is required

Please, help!