duplicate key

I received a beta key 2 hours ago, and when I go to activate it on steam it tell me that it has been used on another account…

There was an issue with duplicate/invalid Steam keys earlier, resulting in codes having to be re-generated and published a few times. 343 have resolved this issue now and distributed new and working codes to everyone affected. If for any reason your new code still does not work, please file a support ticket on the Insider Support Site.

You can check for your new Steam key in one of these three places: