title: Suddenly there is so many errors when I open a new Unity project
body: <p>I've started learning Unity recently, and everything was working fine, then I uninstalled Kaspersky internet security, and then I faced up some problems in Windows but I solved it.<br>
  Then today I wanted to open an old project in Unity that worked fine days ago, and I have a lot of errors like this</p>
  <pre><code>Error: Could not load signature of Packages.Rider.Editor.UnitTesting.TestEvent:.ctor due to: Could not load file or assembly 'nunit.framework, Version=3.5.0.0, Culture=neutral, PublicKeyToken=2638cd05610744eb' or one of its dependencies. assembly:nunit.framework, Version=3.5.0.0, Culture=neutral, PublicKeyToken=2638cd05610744eb type:&lt;unknown type&gt; member:(null) signature:&lt;none&gt;
  </code></pre>
  <p>about 450 errors like that :)
  <a href="https://i.stack.imgur.com/wSRcU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wSRcU.png" alt="unity errors" /></a></p>
  <p>I tried to uninstall the editor and reinstall it, BUT nothing works.<br>
  I also tried to start a new 3D project, and it also ended with the same result.<br>
  the unity editor I used is 2019.4.18f1 Personal<br>
  Need some help pls :(</p>