I have the same problem. I noticed occasionally in matchmaking I would suddenly get booted from the game, with the "disc is Unreadable/dirty disc" error...and always RIGHT at the split second when the map was supposed to first open...not always,only sometimes. Then I pre-ordered Halo CEA. I was super excited to see Breakneck,since I was a HUGE halo 2 guy. When the disc arrived in the mail, I popped it in, put in the code for the map pack, and fired up Breakneck... "Unreadable Disc" Upon further investigation,it turns out that both Breakneck (while EITHER the "Reach" disc, or the "CEA" disc are in the tray)as well as the Reach map "Powerhouse" cause the same error. The funny thing about the latter is that it's a map from the original disc,not DLC that could've become a corrupted file. M$ Support gave me the run around,claiming my case to be "Unique". They tried to goad me into sending my "out of warranty" box in for a "repair",which I refused. They then tried to tell me that the problem might be in my Hard Drive, so the best thing I could do was SEND THEM MY HD, and they would then send me a new one. (???) I explained that I had lots of content on my drive that I didn't want to lose, and that they should just send me a new drive...WHICH THEY DID...YIPPEE ! ! ! ...but it didn't work. I still get the errors after transferring all my old files,and re-downloading the map pack. I believe it was the second most recent Dashboard Update. I think it had something to do with the new "Slim" xbox consoles, and trying to tweak the older consoles' firmware to match the newer models(?)...I read somewhere that it effected how the machine reads the disc(?). But I think the change effected some games (VERY few) but REACH was one of them. I think they are trying to downplay this and hope that they can quietly upgrade warrantied XBOXes, and quietly hope that UN-WARRANTIED box owners sulk away figuring it's their fault for being "Early Adopters", and meekly upgrade to a newer 360 console,before again being slapped with the NEW MODEL in 2014. It's shrewd marketing.