Reference assemblies for framework “.NETFramework,Version=v4.7.1” were not found

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.

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.

So any help is welcome ! 🙂

Unity version : 2018.3.1f1

Logs :

dotnet — info

.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]

mono –version

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

The full log error :

    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

Answer

I had the same issue but on OSX. Installing latest version of Mono cleared up the missing .net v4.7.1 framework references.

I installed Mono V5.18.0 from https://www.mono-project.com/download/stable

Update: See comment below regarding global omnisharp setting