Unable to See IPv6 Logs on Fortigate Firewall

Hi Team, Recently i ahve enable the IPv6 feature on Fortigate900D and I can able to create the ipv6 policies and routing. but i am unable to see any logs on "All session". Can anyone shed somelight how to check the ipv6 policies are allowed or denied. Where can i see the deny ipv6 logs ?   Thanks in Advance.. John Peera