Firstly, make sure ipv6 is enabled on both servers never disable it especially on sbs. Is the R2 server added onto the domain? What happens if you static your IP and then force static the DNS server to your SBS server? Is UAC disbabled or enabled? Try a 'netsh winsock reset' on the R2 server from command prompt then reboot. Lastly try restarting the "server" service and see if you can brwose to it.