NTP not working

Dear, 

We want to use Fortigate NTP as the source to synchronize time in our environment. The configuration seems very simple but unfortunately it is not working. Please find the configuration below...

ROM-FG-80E # show system ntp config system ntp set ntpsync enable set syncinterval 2 set source-ip 192.168.2.254         (LAN interface) set server-mode enable set interface "dmz" "lan" end

ROM-FG-80E # diag sys ntp status synchronized: no, ntpsync: enabled, server-mode: enabled

ipv4 server(ntp2.fortiguard.com) 208.91.112.51 -- unreachable(0x0) S:7 T:8 no data ipv4 server(ntp1.fortiguard.com) 208.91.112.50 -- unreachable(0x0) S:7 T:8 no data ipv4 server(ntp2.fortiguard.com) 208.91.113.71 -- unreachable(0x0) S:7 T:8 no data ipv4 server(ntp1.fortiguard.com) 208.91.113.70 -- unreachable(0x0) S:7 T:8 no data

ROM-FG-80E # execute ping ntp2.fortiguard.com PING ntp2.fortinet.net (208.91.112.51): 56 data bytes 64 bytes from 208.91.112.51: icmp_seq=0 ttl=48 time=239.8 ms 64 bytes from 208.91.112.51: icmp_seq=1 ttl=48 time=238.7 ms 64 bytes from 208.91.112.51: icmp_seq=2 ttl=48 time=238.6 ms 64 bytes from 208.91.112.51: icmp_seq=3 ttl=48 time=239.9 ms 64 bytes from 208.91.112.51: icmp_seq=4 ttl=48 time=238.6 ms

Any ideas on how to troubleshoot this?

Thanks in advace,