We are now experiencing this problem since uploading the Halo Mythic Map Pack. Until then we were able to connect to Halo 3 multiplayer.
After the download we received a notification about changes to accounts and that we had to accept them before proceeding with logging on. We went through the steps and now none of the accounts can access multiplayer.
When attempting to access Halo multiplayer the following message appears: one of the accounts is not able to access multiplayer online and this will affect all of the accounts associated with our 360 accounts.
We changed the family settings, but this didn't work.
We reviewed/changed each of the accounts associated with our 360, but this didn't work. We also removed accounts, but this didn't help either. I tried recovering my gamertag, but this didn't work. I tried creating a new Live account, but this didn't work. (Running out of options ... what should I try?)
We can log on to Live, but we cannot access multiplayer. Any suggestions would be welcomed. (We have logged an email support request.)