title: Back port .NET 4 to 3.5 SP1 in VS2010
body: <p>I wrote a simple VS2010 WPF application which targeted <strong>.NET Framework 4 Client Profile</strong>. (In fact, my app does not use any .NET 4 features, but VS2010 just by default started my project targeting .NET 4 so I didn't bother to check it)</p>
  
  <p>I found all XP system and even a few Window 7 of various languages failed to start the app. I decided to back port my app to target <strong>.NET Framework 3.5</strong> or <strong>.NET Framework 3.5 Client Profile</strong>, by changing the <code>Target Framework</code> in solution's properties. But the app does not compile or build with the following error on <code>System.Xaml</code> and <code>Microsoft.CSharp</code>:</p>
  
  <pre><code>Warning 1   Could not resolve assembly System.Xaml. The target framework required by this assembly (4.0) is higher than the project target framework. If this reference is required by your code, you may get compilation errors.   test1
  Warning 2   The primary reference "Microsoft.CSharp", which is a framework assembly, could not be resolved in the currently targeted framework. ".NETFramework,Version=v3.5". To resolve this problem, either remove the reference "Microsoft.CSharp" or retarget your application to a framework version which contains "Microsoft.CSharp".    test1
  Warning 3   The referenced component 'Microsoft.CSharp' could not be found.     
  Warning 4   The referenced component 'System.Xaml' could not be found.  
  </code></pre>
  
  <p>Is it possible to back port (or back target) a VS2010 app to .NET 3.5? If so, how?</p>
  
  <p><strong>[EDIT]</strong></p>
  
  <p>I found there was one Control - DataGrid - that is designed to use for .NET 4. I have to install WPF Tool Kit to back port the controls to 3.5. Hope someone find this helpful.</p>