Call to Ring group rejected

Hi,
Having this problem a few times, extension to extension call was ok but not extension call to ring group. We got call rejected when call to the ring group.
If we restarted using “/etc/init.d/asterisk restart” command also not working. Only after restart with command amprotal restart, then the ring group is working. Anyone having this problem ?

Asterisk version : 1.8.12.0
Freepbx : 2.10

Thanks