title: Upgrade to 2019.2.13 causes Namespace name `EventSystems' could not be found
body: <p>I have upgraded from 2018.3.14f to 2019.2.13 and I started having really strange errors.</p>
  
  <p>I am now having those two errors:</p>
  
  <blockquote>
    <p>The type or namespace name <code>EventSystems' does not exist in the namespace</code>UnityEngine'. Are you missing an assembly reference?</p>
  </blockquote>
  
  <p>and</p>
  
  <blockquote>
    <p>The type or namespace name <code>UI' does not exist in the namespace</code>UnityEngine'. Are you missing an assembly reference?</p>
  </blockquote>
  
  <p>This is happening only to the project which I upgraded from 2018.3.14 to 2019.2.13.</p>
  
  <p>If I create a new blank project with 2019 there is no issue. The namespaces are found plus when I go to <code>New2019Project/Library/ScriptAssemblies/</code> I can see the following files:</p>
  
  <p><a href="https://i.stack.imgur.com/2bjsi.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2bjsi.png" alt="enter image description here"></a></p>
  
  <p>Then If I go to my upgraded old project in this dir <code>OldUpgradedTo2019Project/Library/ScriptAssemblies/</code> the folder is having only those files:</p>
  
  <p><a href="https://i.stack.imgur.com/CfJra.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/CfJra.png" alt="enter image description here"></a></p>
  
  <p>As you can see I don't have those files in my updated project. If I try to copy the ones from the new working one into my old upgraded, at the time I start the Unity for the upgraded old project it deletes them and the problem stays.</p>
  
  <p>Is there any way I can fix this annoying problem?</p>