title: Why might System.Threading.dll be missing from Windows\Assembly?
body: <p>I've various versions of the .NET Framework (versions 1.1 thru 4.0) installed on a remote machine running XP Professional. I've installed Reactive Extension too for good measure. </p>
  
  <p>I also have an application which works on my machine because it references System.Threading found here:
  C:\Program Files\Microsoft Reactive Extensions\redist\desktopV2\System.Threading.dll</p>
  
  <p>I have two versions of the DLL in the GAC also.</p>
  
  <p>Two questions:</p>
  
  <p>i) Why did Visual Studio decide that this is the version (instance) to reference when I chose from the list rather than browsing to to the file?</p>
  
  <p>ii) Why does System.Threading not exist on the remote machine? 
  (I thought it was a core part of the Framework)</p>
  
  <p>Thanks</p>