Mixed mode assembly is built against version ‘v2.0.50727′ of the runtime
Try to use this exact startup tag in your app.config under configuration node
<startup useLegacyV2RuntimeActivationPolicy="true">
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
<requiredRuntime version="v4.0.20506" />
</startup>
The exception clearly identifies some .NET 2.0.50727 component was included in .NET 4.0. In App.config file use this:
<startup useLegacyV2RuntimeActivationPolicy="true" />
It solved my problem