I have a remote site connected to my LAn via IPsec tunnel.
From the remote site (192.168.x.x) I have a server that can ping all the other servers on my LAN (10.1.0.0) except the Asterisk server.
From the LAN I can ping the remote server and a Linksys spa941 phone I have on the remote site. I can even manage the phone from a web browser on the LAN.
The phone therefore can not get to the Asterisk server, nor can the Asterisk server be pinged from the remote network.
The only difference on the Asterisk servers networking is that it has a default gateway of 10.1.0.252 on the LAN whereas all the other servers have a default gateway of 10.1.0.254.