Norton/Symantec Personal Firewall is one of the more problematic ones when it comes to running OpenVPN.
Errors you may encounter:
Sat Jan 23 20:59:31 2010 write UDPv4: The requested address is not valid in its context. (code=10049)
Sat Jan 23 20:45:11 2010 RESOLVE: Cannot resolve host address: vpn.12vpn.com: [HOST_NOT_FOUND] The specified host is unknown.
We highly recommend you upgrade to a better firewall solution. If this is not possible, please try turning off the Stealthy Ports option in the Personal Firewall Advanced Settings.
Alternatively you can try to uninstall the firewall, connect to the VPN and, while connected, re-install the firewall.