Clients are able to connect to Guest, they are receiving a valid private IP, the browser is not redirecting to the captive portal. I have this exact setup elsewhere, and its working fine.
amigopod: Failed RADIUS dynamic authorization for user '00:18:de:3e:47:6f': Internal error: No RADIUS authentication server with ID : IP-Addr '172.16.11.182' Calling '0018DE3E476F' Called 'D8C7C8C6AC0B' Start '2012-03-28T12:42:58-04:00' Seq 729 NAS-IP-Address 'xxx.xxx.xxx.xxx' NAS-Identifier '\"slap01 (Virtual Controller)\"' RADIUS-Client xxx.xxx.xxx.xxx'