title: C# Predefined type 'System.Object' is not defined or imported
body: <p>In <strong>.NET core</strong> project, I changed the all projects name than after reloading all project that time many errors were showing approx <strong>3225</strong>. And mainly all errors are related to system namespace like </p>
  
  <ul>
  <li><code>System.Object</code> not defined or imported </li>
  <li><code>System.Boolean</code> not defined or imported </li>
  <li><code>Task</code> does not exist</li>
  <li>namespace <code>ArgumentNullException</code> could not be found</li>
  </ul>
  
  <p>How do I resolve all those errors?</p>