title: Feature 'using declarations' is not available in C# 7.3. Please use language version 8.0 or greater - Error on one machine but works on another
body: <p>When using <strong>Visual Studio Enterprise 16.3.7</strong> on two separate machines, one builds fine and the other machine throws the error:</p>
  <blockquote>
  <p>Feature 'using declarations' is not available in C# 7.3. Please use
  language version 8.0 or greater.</p>
  </blockquote>
  <p><a href="https://i.stack.imgur.com/RC2Rv.png" rel="noreferrer"><img src="https://i.stack.imgur.com/RC2Rv.png" alt="enter image description here" /></a></p>
  <p><a href="https://i.stack.imgur.com/lnu10.png" rel="noreferrer"><img src="https://i.stack.imgur.com/lnu10.png" alt="enter image description here" /></a></p>
  <p>This can easily be solved on the non-working machine by setting <code>LangVersion</code> in <code>.csproj</code> as suggested here <a href="https://stackoverflow.com/a/48085575/3850405">https://stackoverflow.com/a/48085575/3850405</a> or let Visual Studio automatically fix it like the screenshot above.</p>
  <pre class="lang-xml prettyprint-override"><code>&lt;LangVersion&gt;8.0&lt;/LangVersion&gt;
  </code></pre>
  <p>What I can't understand is why one machine builds fine without this line in <code>.csproj</code> and the other machine needs it?</p>