disc read error w/ game already loaded to HD

When a game is installed to the hard drive the majority of the game's content is installed, but the physical disc is still required, and needs to be in good condition to work, as the game still accesses it. Requiring the disc to be in the tray prevents game piracy, ultimately. Installing a game reduces load times and increases ease of access for glitchy games. 

If the disc is badly scratched, warped, or damaged the game will not play, despite the content install. Clean the disc with a soft/specially designed rag wiping from the center out. Use only a tiny amount of water on the cloth. If the scratches are deeper, contact your local video stores to see if they offer a buffering service, as most chain rental places possess a disc buffer.

 Thanks Monosocratic,

I was thinking perhaps the disc needed to be accessed periodically. However the disc is a brand new copy of Brink and has since been exchanged for a new copy which is having similar problems. The new patch hasn't helped me and alot of other people from what I've been reading so I'll just keep trying each day to see if things improve. I think there are multiple possible factors working against this game right now. I think for it to function properly a xbox360 with a fresh drive and a solid high speed connection are required. that being said there are actually patches needed for all platforms that this game runs on, PS3, PC, XBOX360 and probably MAC too if its available for that platform.

try cleaning your disc drives optics dust can cause it to this as can something as small as a finger print.

Most likely dust.  This happened to my new copy of Far Cry 3 a couple times.  Disc was clean so the lens must of had a speck of dust on it.