title: easiest way to convert .NET project from 4.5 to 4.0?
body: <p>I have a .NET application that I built in 4.5, which has references to a bunch of libraries that were built in 4.5, which themselves have references to 4.5, etc.  A user group that I'm trying to distribute the application to is having problems running the executable because they have 4.0 installed; in particular, they're getting a MissingMethodException:</p>
  
  <pre><code>Method not found: 'System.Type System.Runtime.InteropServices.Marshal.GetTypeFromCLSID(System.Guid)'.
  </code></pre>
  
  <p>Because we may have trouble getting each user upgraded to 4.5 (as none of them have admin permissions on their machines and this would require a separate upgrade request for each user), I'm looking at finding an easy way to rebuild the project as 4.0.  This seems to require that I rebuild every library and its referenced libraries in 4.0; is there an easier way to do this than going through each library one by one and building a 4.0 version?  I'm thinking maybe like a one-click option for "Rebuild all referenced libraries in target framework" or something like that.</p>