title: MSBuild "Unable to copy file" in CI environment
body: <p>I'm using Hudson as a continuous integration server.  The jobs ultimately kick off MSBuild.  Everyone once in a while, my build fails with a non-code-compilation error out of MSBuild:</p>
  
  <pre><code>C:\WINDOWS\Microsoft.NET\Framework\v3.5\Microsoft.Common.targets(2703,9): error MSB3021: Unable to copy file "..\Lib\Microsoft\Microsoft.Practices.Unity.Configuration.dll" to "bin\Debug\Microsoft.Practices.Unity.Configuration.dll". Access to the path 'bin\Debug\Microsoft.Practices.Unity.Configuration.dll' is denied.
  </code></pre>
  
  <p>When I examine 'bin\Debug\Microsoft.Practices.Unity.Configuration.dll', I find it to be a 0-byte file.</p>
  
  <p>I'm at a loss for why this file is being problematic.  Any ideas?</p>