[asterisk-users] Asterisk 1.8 - SIP losing registration

[Joseph]

After upgrade to Asterisk 1.8 one of my phones connected to AudoCodes box is losing SIP registration.
I can call out but when I tray to call that extension it ring busy.
Other times when I call this extension the phone rings and when I hang up the phone still keep ringing, it does not disconnect.

Any idea what to look for?

-- 
Joseph