title: Unity blank compiler errors with no details
body: <p>On a new, very basic project I was working on, I suddenly started getting blank compiler errors with no details about what <em>actually</em> has gone wrong. If I start a new project, that project will also have these errors. I figured out that the only difference between these new projects and my old ones (which still work, load, and compile without any errors) was that the %project%/Library/ScriptAssemblies/ directory is empty.</p>
  
  <p>Copying the contents of that directory from an older project into the newer one will make the errors go away temporarily on a project that has NO scripts in it - The moment I include a script the project becomes unusable again. I have spent all day googling this every way conceivable and yet I cannot find any information that actually helps me solve this problem. Most links are unrelated or don't contain useful info.</p>
  
  <p>The error is as follows:</p>
  
  <pre><code>Microsoft (R) Visual C# Compiler version 2.9.1.65535 (9d34608e)
  Copyright (C) Microsoft Corporation. All rights reserved.
  </code></pre>
  
  <p>There is NO additional detail to help me figure out what went wrong. That is the entire error. Appears 4x in console prior to copying that directories contents, afterwards it only appears once. This is what appears in Editor.log;</p>
  
  <pre><code> -----CompilerOutput:-stdout--exitcode: 1--compilationhadfailure: True--outfile: Temp/Assembly-CSharp.dll
  Microsoft (R) Visual C# Compiler version 2.9.1.65535 (9d34608e)
  Copyright (C) Microsoft Corporation. All rights reserved.
  
  -----CompilerOutput:-stderr----------
  The system cannot find the path specified.
  -----EndCompilerOutput---------------
  - Finished compile Library/ScriptAssemblies/Assembly-CSharp.dll
  Microsoft (R) Visual C# Compiler version 2.9.1.65535 (9d34608e)
  Copyright (C) Microsoft Corporation. All rights reserved.
  </code></pre>
  
  <p>I have (unsuccessfully) tried;<br>
    - Changing scripting runtime version<br>
    - Changing scripting backend<br>
    - Changing API compatibility level<br>
    - Deleting all META files from assets and reloading project<br>
    - Reimporting all assets<br>
    - Restarting Unity after forcibly closing ALL related tasks
    - Installing a new version of Unity (2019.3) and starting a NEW project.</p>
  
  <p>Unity Version is 2019.1, I have both VS2015 and VS community 2017 installed.</p>