MSBuild conflict between mscorlib 4.x and mscorlib 2.x
<p>I was investigating a build failure recently and saw a warning about conflicts between assemblies. I dug deeper and MSBuild told me this: </p>

<blockquote>
  <p>There was a conflict between "mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" and "mscorlib, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e, Retargetable=Yes".
        "mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" was chosen because it was primary and "mscorlib, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e, Retargetable=Yes" was not.`</p>
</blockquote>

<p>My solution contains several console applications, lots of class libraries and ASP.NET application. We build on .NET 4.5.2.</p>

<p>Should I be concerned?</p>