[asterisk-users] WARNING[19164] chan_sip.c: Forbidden - wrong password on authentication for INVITE to '"unknown" <sip:unknown at xxx.xxx.xxx.xxx>

[gincantalupo]

Hi,
I'm using an Asterisk 1.2.18 box with a remote Snom 360. My Snom always 
rings but sometimes (it happens randomly!) no voice is passing thru (2 
ways).
Asterisk CLI shows this warning:

Jan 10 10:03:26 WARNING[19164] chan_sip.c: Forbidden - wrong password on 
authentication for INVITE to '"unknown" <sip:unknown at xxx.xxx.xxx.xxx>

I have already set localnet and externip parameters inside the general 
section of my sip.conf:
localnet = 192.168.4.0/24
externip = xx.xx.xx.xxx

Is there anybody who knows how to solve this problem?

Thank you!