title: Every C# script is throwing errors on the console
body: <p>I've just created an Unity project with a clean installation, also created a C# script and attached to a 3D Game Object (Cube), but when I double-click to open the script it instantly says: </p>
  
  <pre><code>Exception thrown while invoking [OnOpenAssetAttribute] method 'Unity.CodeEditor.CodeEditor:OnOpenAsset (int,int,int)' : InvalidOperationException: Cannot start process because a file name has not been provided.
  System.Diagnostics.Process.Start () (at &lt;d465e2b2e5054d2787d6364114c43446&gt;:0)
  (wrapper remoting-invoke-with-check) System.Diagnostics.Process.Start()
  UnityEditor.DefaultExternalCodeEditor.OpenProject (System.String path, System.Int32 line, System.Int32 column) (at C:/buildslave/unity/build/Editor/Mono/CodeEditor/DefaultExternalCodeEditor.cs:96)
  Unity.CodeEditor.CodeEditor.OnOpenAsset (System.Int32 instanceID, System.Int32 line, System.Int32 column) (at C:/buildslave/unity/build/Editor/Mono/CodeEditor/CodeEditor.cs:56)
  UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)
  </code></pre>
  
  <p>and </p>
  
  <pre><code>InvalidOperationException: Cannot start process because a file name has not been provided.
  System.Diagnostics.Process.Start () (at &lt;d465e2b2e5054d2787d6364114c43446&gt;:0)
  (wrapper remoting-invoke-with-check) System.Diagnostics.Process.Start()
  UnityEditor.DefaultExternalCodeEditor.OpenProject (System.String path, System.Int32 line, System.Int32 column) (at C:/buildslave/unity/build/Editor/Mono/CodeEditor/DefaultExternalCodeEditor.cs:96)
  Unity.CodeEditor.CodeEditor.OpenFileAtLineColumn (System.String path, System.Int32 line, System.Int32 column) (at C:/buildslave/unity/build/Editor/Mono/CodeEditor/CodeEditor.cs:31)
  UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)
  </code></pre>
  
  <p>And if I, for example, try to use <code>Debug.Log</code> in the script, it says </p>
  
  <pre><code>'Debug' does not contain a definition for 'Log'
  </code></pre>
  
  <p>Nothing works.</p>
  
  <p>I've already tried to reopen unity, create another project, install another version (I'm now using the latest 2019.2.0b1) and this always happens, I'm using Visual Studio and the errors are prompted in the Unity console.</p>