title: Reference assemblies for framework ".NETFramework,Version=v4.7.1" were not found
body: <p>I try to open a Unity3D project with VSCode under Linux (Ubuntu 18.10). The omnisharp extension doesn't load the project, saying assemblies were not found.</p>
  
  <p>It may seems very stupide, but i'm not really used to .Net yet, and i have been stuck with this error for quite some days now.
  I have been trying re-installing dotnet (even using the snap package), mono, vscode and the omnisharp extension.</p>
  
  <p>So any help is welcome ! :)</p>
  
  <p>Unity version : 2018.3.1f1</p>
  
  <p><strong>Logs :</strong></p>
  
  <p><strong>dotnet -- info</strong></p>
  
  <pre><code>.NET Core SDK (reflecting any global.json):
   Version:   2.2.103
   Commit:    8edbc2570a
  
  Runtime Environment:
   OS Name:     ubuntu
   OS Version:  18.10
   OS Platform: Linux
   RID:         ubuntu.18.10-x64
   Base Path:   /usr/share/dotnet/sdk/2.2.103/
  
  Host (useful for support):
    Version: 2.2.1
    Commit:  878dd11e62
  
  .NET Core SDKs installed:
    2.2.103 [/usr/share/dotnet/sdk]
  
  .NET Core runtimes installed:
    Microsoft.AspNetCore.All 2.2.1 [/usr/share/dotnet/shared/Microsoft.AspNetCore.All]
    Microsoft.AspNetCore.App 2.2.1 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
    Microsoft.NETCore.App 2.2.1 [/usr/share/dotnet/shared/Microsoft.NETCore.App]
  </code></pre>
  
  <p><strong>mono --version</strong></p>
  
  <pre><code>Mono JIT compiler version 4.6.2 (Debian 4.6.2.7+dfsg-1ubuntu1)
  Copyright (C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
      TLS:           __thread
      SIGSEGV:       altstack
      Notifications: epoll
      Architecture:  amd64
      Disabled:      none
      Misc:          softdebug 
      LLVM:          supported, not enabled.
      GC:            sgen
  </code></pre>
  
  <p><strong>The full log error :</strong></p>
  
  <pre><code>    Starting OmniSharp server at 1/26/2019, 7:13:55 PM
      Target: /home/eyap/Projects/Unity/TestProject/TestProject.sln
  
  OmniSharp server started.
      Path: /home/eyap/.vscode/extensions/ms-vscode.csharp-1.17.1/.omnisharp/1.32.8/run
      PID: 30136
  
  [info]: OmniSharp.Stdio.Host
          Starting OmniSharp on ubuntu 18.10 (x64)
  [info]: OmniSharp.Services.DotNetCliService
          DotNetPath set to dotnet
  [info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
          Located 1 MSBuild instance(s)
              1: StandAlone 15.0 - "/home/eyap/.vscode/extensions/ms-vscode.csharp-1.17.1/.omnisharp/1.32.8/omnisharp/msbuild/15.0/Bin"
  [info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
          MSBUILD_EXE_PATH environment variable set to '/home/eyap/.vscode/extensions/ms-vscode.csharp-1.17.1/.omnisharp/1.32.8/omnisharp/msbuild/15.0/Bin/MSBuild.dll'
  [info]: OmniSharp.MSBuild.Discovery.MSBuildLocator
          Registered MSBuild instance: StandAlone 15.0 - "/home/eyap/.vscode/extensions/ms-vscode.csharp-1.17.1/.omnisharp/1.32.8/omnisharp/msbuild/15.0/Bin"
              MSBuildExtensionsPath = /home/eyap/.vscode/extensions/ms-vscode.csharp-1.17.1/.omnisharp/1.32.8/omnisharp/msbuild
              BypassFrameworkInstallChecks = true
              CscToolPath = /home/eyap/.vscode/extensions/ms-vscode.csharp-1.17.1/.omnisharp/1.32.8/omnisharp/msbuild/15.0/Bin/Roslyn
              CscToolExe = csc.exe
              MSBuildToolsPath = /home/eyap/.vscode/extensions/ms-vscode.csharp-1.17.1/.omnisharp/1.32.8/omnisharp/msbuild/15.0/Bin
              TargetFrameworkRootPath = /usr/lib/mono/xbuild-frameworks
  [info]: OmniSharp.Cake.CakeProjectSystem
          Detecting Cake files in '/home/eyap/Projects/Unity/TestProject'.
  [info]: OmniSharp.Cake.CakeProjectSystem
          Could not find any Cake files
  [info]: OmniSharp.WorkspaceInitializer
          Project system 'OmniSharp.DotNet.DotNetProjectSystem' is disabled in the configuration.
  [info]: OmniSharp.MSBuild.ProjectSystem
          Detecting projects in '/home/eyap/Projects/Unity/TestProject/TestProject.sln'.
  [info]: OmniSharp.MSBuild.ProjectManager
          Queue project update for '/home/eyap/Projects/Unity/TestProject/Assembly-CSharp.csproj'
  [info]: OmniSharp.Script.ScriptProjectSystem
          Detecting CSX files in '/home/eyap/Projects/Unity/TestProject'.
  [info]: OmniSharp.Script.ScriptProjectSystem
          Could not find any CSX files
  [info]: OmniSharp.WorkspaceInitializer
          Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpWorkspaceOptionsProvider
  [info]: OmniSharp.WorkspaceInitializer
          Configuration finished.
  [info]: OmniSharp.Stdio.Host
          Omnisharp server running using Stdio at location '/home/eyap/Projects/Unity/TestProject' on host 30056.
  [info]: OmniSharp.MSBuild.ProjectManager
          Loading project: /home/eyap/Projects/Unity/TestProject/Assembly-CSharp.csproj
  [fail]: OmniSharp.MSBuild.ProjectLoader
          The reference assemblies for framework ".NETFramework,Version=v4.7.1" were not found. To resolve this, install the SDK or Targeting Pack for this framework version or retarget your application to a version of the framework for which you have the SDK or Targeting Pack installed. Note that assemblies will be resolved from the Global Assembly Cache (GAC) and will be used in place of reference assemblies. Therefore your assembly may not be correctly targeted for the framework you intend.
  [warn]: OmniSharp.MSBuild.ProjectManager
          Failed to load project file '/home/eyap/Projects/Unity/TestProject/Assembly-CSharp.csproj'.
  /home/eyap/Projects/Unity/TestProject/Assembly-CSharp.csproj
  /home/eyap/.vscode/extensions/ms-vscode.csharp-1.17.1/.omnisharp/1.32.8/omnisharp/msbuild/15.0/Bin/Microsoft.Common.CurrentVersion.targets(1195,5): Error: The reference assemblies for framework ".NETFramework,Version=v4.7.1" were not found. To resolve this, install the SDK or Targeting Pack for this framework version or retarget your application to a version of the framework for which you have the SDK or Targeting Pack installed. Note that assemblies will be resolved from the Global Assembly Cache (GAC) and will be used in place of reference assemblies. Therefore your assembly may not be correctly targeted for the framework you intend.
  
  [fail]: OmniSharp.MSBuild.ProjectManager
          Attemped to update project that is not loaded: /home/eyap/Projects/Unity/TestProject/Assembly-CSharp.csproj
  </code></pre>