Symantec 320 VPN appliance intermittent connectivity

[Lwanga]

We have a gateway to gateway VPN connecting 2 lans using the Symantec SGS 320 VPN appliance at both ends. The VPN connectivity between sites (ping, drive mapping, database sharing work OK) only last for about 20 minutes before the appliance need to be rebooted at Site Y. Even though the VPN connection does not last, users never lose internet or POP3 connectivity. The timeout is set to 0 at both ends and all other configurations are standard.

Both sites are colocated in office buildings that provide them with public IPs on their lans.

Site X
     
   internal            external
              |---|
--192.162.4.1-|   |--213.xxx.xxx.xxx--lan--ISP--internet


Site Y

    internal           external
                |---|
--192.162.1.1-|   |--65.xxx.xxx.xxx--lan--wan--internet

I have spent alot of time troubleshooting this issue with Symantec, without any solution. Any suggestions would be greatly appreciated.