Brotherhood patch disables multiplayer

Apparently affects only 360 players
However, the good news is that the glitch known as the “Animus” bug has apparently been fixed, as well as a number of other issues that players had been complaining about.
Reports confirm that the Ubisoft Montreal team that is responsible for Assassin’s Creed is aware of the problem and is asking for patience while a fix is prepared to address the multiplayer issue for Xbox 360 owners.
According to several sources, a revision to the patch was introduced later that seems to have fixed the issues with the Xbox 360 multiplayer modes of Brotherhood, but some users are still apparently reporting problems. According to the latest we have, a re-download of the patch will apparently resolve the issue; and it does seem to have worked for us, as we no longer have this problem.