Frankie writes:

UPDATE: In some cases, users are experience a lack of fonts or characters in the user interface after downloading today's update. If this happens to you, all hope is not lost, do not despair, do not run around screaming.

Instead, do the following.
First, restart your Xbox 360.
Second, boot up the Halo 3 beta.
Third, while in the Halo 3 boot up sequence press up on the D-pad and hold the A button until you see the BUNGIE logo. If you've completed this correctly there will be a dialog box confirming maintenance has been done on your system.
Four, resume bathing in the Halo 3 Public Beta.

Last night we made the first test update to the Halo 3 Public Beta, basically a test to ensure that we are able to make subtle or dramatic changes to the game on the fly, in order to react to problems we could encounter going forward. In this case, the change was both subtle and dramatic going as far as invalidating your existing saved films and wiping your file share in advance of tomorrow's public rollout. You must accept and install the tiny update to continue playing correctly.

Don't worry, we will try to keep these updates to a minimum throughout the course of the Beta, and naturally we don't plan to wreck your films everytime a change is made to the game - but in order to implement and test that stuff for the shipping game, this is one of the wee sacrifices we have to make.

Also, due to player response we've also significantly reduced the appearance of Team Slayer gametypes on the Team Skirmish playlist - this means more High Ground CTF for Beta gamers.

Thanks for both your patience and great feedback and stay tuned to Bungie.net for more updates throughout the Beta.