title: NuGet unable to find the version of a package
body: <p>Running the command</p>
  <pre><code>nuget.exe restore .\MySolution.sln
  </code></pre>
  <p>gives this error:</p>
  <blockquote>
  <p>Unable to find version '1.0.0' of package 'Microsoft.Net.Compilers'.</p>
  </blockquote>
  <p>where the package has previously been installed and restored, but it has somehow become corrupt.</p>