Lately I’ve been diving into the new build engine in TFS 2015 RC (RTM release is planned for 20th of July). While running a build, I got the following error message: Mixed mode assembly is built against version ‘v2.0.50727’ of the runtime and cannot be loaded in the 4.0 runtime without additional configuration information. This got me puzzled for a while, especially since the build continued to run and it was doing what it was supposed to do, except that at the end the build turned red because of this error.