Phone forwarding can not hear and auto off?

I install fresh new server have
1 extension.
1 group
call in go to default group 600
in group extension list have
extension 100
phone number format xxxxxxxxx#
out side call in phone xxxxxxxxx# ring but can not talk
internal extension pickup and talk well

I have 4 servers all have same problem, just happen couples days ago.
what do I have to do next. thank for your help