'v2.0.50727' of the runtime and cannot be loaded in the 4.0 runtime without additional configuration information [duplicate]

Answer 1

Open each project's properties - and set version to either 2.0/3.0/3.5 or 4.0

Answer 2

Try to use another config file (not the one from your project) and RESTART Visual Studio:

C:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\IDE\CommonExtensions\Microsoft\TestWindow\vstest.executionengine.x86.exe.config (32-bit)

or

C:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\IDE\CommonExtensions\Microsoft\TestWindow\vstest.executionengine.exe.config (64-bit)

Answer 3

Add this to your web/app config:

<startup useLegacyV2RuntimeActivationPolicy="true">
  <supportedRuntime version="v4.0"/>
</startup>

Also see here

Answer 4

I added the following:

<startup useLegacyV2RuntimeActivationPolicy="true">
  <supportedRuntime version="v4.0"/>
  <requiredRuntime version="v4.0.20506"/>
</startup>

to my app.config for a VS2008 Express Edition to VS2010 Express Edition imported project. Worked fine for me.