BioWare is working to fix the bug that prevents the new Mass Effect DLC Pinnacle Station from being registered by the game - and therefore played.
The glitch occurs because of a conflict between the previous DLC, Bring Down the Sky, and Pinnacle Station. However, only the disc-based version of Bring Down the Sky appears to have this problem. That means only those who bought the Xbox 360 Classics or Platinum Hits version of Mass Effect, which includes the first DLC add-on on-disc, are at risk.
To clarify: if you bought and downloaded Bring Down the Sky from Xbox Live Marketplace then you should be OK.
"We talked to Microsoft quite a bit today, they were able to reproduce the issue and it looks like something that's nearly impossible to catch until it happens," added Lamden.
"I haven't really looked into whose fault the issue is, just what the fault in the software is and how it can get fixed quickly."
Interestingly, Mass Effect PC developer Demiurge made Pinnacle Station and had only "support" from BioWare, which may explain the lack of advertising or fuss made over the new content.
Pinnacle Station costs 400 Microsoft Points (Ł3.40/€4.80) and should also work without incident for people without any existing Mass Effect DLC.