If you're getting errors about missing executables or not being able to download files, it's most likely because the beta build is over and now inaccessible. The build was only supposed to run for the month of October and no longer. So chances are that the files for the build have been taken down from the Steam servers, or at least that's my assumption.
Also don't be that guy who just rattles on about the developers not giving a damn for no good reason. It's incredibly rude.
Where was this announced? I've been trying to follow the development of this game, but I can't remember anything about the beta being timed. Why was it not annouced in the Steam news feed for instance? That would make everyone with the game installed see it.
When the game suddenly stops working, my only assumption can be that something has gone severely wrong, and the lack of any response just angered me.
They posted that information on the Kickstarter page via updates near the beginning of October. But I imagine they couldn't do it via the Steam News Feed because it technically isn't in the Steam store yet, which disables the use of the News Feed. Though I'm surprised you didn't see any information on it. I'm guessing you bought it directly via Paypal or something of the sort?