A thread on the BioWare Social Network describes problems with the recently released Lair of the Shadowbroker DLC for Mass Effect 2, which is no longer available for purchase while they work on fixing it. Here's the word:

People using Xbox Live for the Xbox 360 can download and play Lair of the Shadowbroker. If you are an Xbox 360 user, please go ahead and enjoy the new DLC.

PC users currently are experiencing a technical issue with the downloaded file that prevents ALL PC users from playing the DLC. We are aware of this issue and have taken the following steps:

        • We have removed the incorrect file from the download section so no further incorrect downloads will occur

        • We are working on a fix for the issue and will get a working file up for PC users ASAP

More detail
If you downloaded the incomplete file (it is essentially 1.5 Gig of zeroes) this will not harm your system
You will NOT be charged again once the correct file is ready for download
We do not have a more accurate eta for the correct PC DLC, but when we do I will let you know.

As soon as we have more information I will post it here. We are sorry that this occured and we appreciate your patience as we work to get the fix to you.