Halo CE Multiplayer doesn't work when Parental controls enabled

My son bought Halo Combat Evolved and installed it after we upgraded his PC
to Vista. He could never attach to Multiplayer games - He could get a list
of active games, but when he tried to connect, it timed out - no response.
After trying several things, we disabled parental controls, and it worked
immediately.

The only thing we have blocked in parental controls is pornography web
sites... all the games, no matter the rating, and unrated, are enabled.
Single player Halo works fine, just Multiplayer is broken.

He has installed all the latest Halo patches. Any ideas how to keep
parental controls working, yet allow Multiplayer? I haven't found any
details about parental controls that describe preventing online collaboration
games.