Try running the “Stealth Ports Wizard” and make the IP addresses of the other computers on your network trusted.
Go to Firewall/Common Tasks/Stealth Ports Wizard->The top box “Define a new trusted network, stealth my ports to everyone else” is allways checked when you enter this, just click “Next”
Now check “I would like to define and trust a new network zone”, add the starting and ending IPs of the addresses you wish to access and then click "Finish" You should receive the message "Your firewall has been configured accordingly" and if you look in Network security policy you will see 2 rules under System for the IPs and 2 in Global rules.