With the limited information you have provided, it's very difficult to offer suggestions.
That said, have you tried the phone on a different network, not behind the Cisco RV? I know I have seen SIP issues with different specific models of phones on certain routers.
You also need to confirm the NAT configuration of the Asterisk box you are trying to connect to. Xlite and other hardware phones use STUN and mangle their contact header to work around NAT issues, and Polycoms don't do this, so if your NAT configuration is wrong on the server, it will fail to connect.