The Microsoft .NET Framework is a programming and run-time environment that runs on Microsoft Windows. Programs written for the .NET Framework execute in a software environment known as the Common Language Runtime (CLR). The CLR is an application virtual machine instead of accessing the hardware directly. A program written for .NET requires that the .NET framework must be installed before the new program can run. source: wikipedia.org
Many of the 2012 and 2013 family of products use version 4 of the .NET Framework. As Through the Interface blogger, Kean Walmsley, has pointed out: .NET 4.0 implements slightly more stringent security than prior versions of the framework: if a Dynamically Loadable Library (DLL) is suspected as having been downloaded from the web – as is clearly the case with our technology previews – the .NET 4.0 runtime will treat that DLL as if it has been loaded from a network share. And as many of you have found out, from trying to load DLLs from network shares, this results in a reduced set of privileges on the local machine, which can often result in a load error.
In other words, since the technology preview is being installed to your machine as an addition, Windows worries about what it might do to your system. To be safe, Windows limits what it can do. In the case of Autodesk Labs technology previews, you can let Windows know that you want the technology preview to be able to operate fully.
Kean recommended a solution: you simply need to “Unblock” the DLL by right-clicking on it in Explorer and selecting “Properties” and “Unblock”. It’s actually better to do this for the .ZIP prior to extracting the contents, as this makes sure all files contained in the archive are unblocked.
Unblocking a technology preview for 2012 or 2013 is alive in the lab.