help with vnc


i have just installed comodo firewall and i have 2 machines, i am able to connect to machine 2 from machine 1 but unable to connect to machine 1 from machine 2. i donot get any alert asking me to create rule jus like i got when i was connected to machine 2 from machine 1.

i am using windows xp sp2 on both and i am using realvnc on both.