Unable to load the project after the SDK was upgraded to .NET 5.0

Environment data

dotnet --info output:

.NET SDK (reflecting any global.json):
 Version:   5.0.100     
 Commit:    5044b93829  

Runtime Environment:    
 OS Name:     Windows   
 OS Version:  10.0.19041
 OS Platform: Windows   
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\5.0.100\

Host (useful for support):
  Version: 5.0.0
  Commit:  cf258a14b7

.NET SDKs installed:
  3.1.100 [C:\Program Files\dotnet\sdk]
  3.1.101 [C:\Program Files\dotnet\sdk]
  3.1.201 [C:\Program Files\dotnet\sdk]
  3.1.301 [C:\Program Files\dotnet\sdk]
  5.0.100 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.All 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.5 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 5.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET runtimes or SDKs:
  https://aka.ms/dotnet-download```

VS Code version:
C# Extension version:

## OmniSharp log
```OmniSharp.MSBuild.ProjectManager
        Failed to load project file 'c:\Projects\i21RESTfulApi\i21RESTfulApi.csproj'.
c:\Projects\i21RESTfulApi\i21RESTfulApi.csproj(1,1)
Microsoft.Build.Exceptions.InvalidProjectFileException: The SDK 'Microsoft.NET.Sdk.Web' specified could not be found.  c:\Projects\i21RESTfulApi\i21RESTfulApi.csproj
   at Microsoft.Build.Shared.ProjectErrorUtilities.ThrowInvalidProject(String errorSubCategoryResourceName, IElementLocation elementLocation, String resourceName, Object[] args)
   at Microsoft.Build.Evaluation.Evaluator`4.ExpandAndLoadImportsFromUnescapedImportExpressionConditioned(String directoryOfImportingFile, ProjectImportElement importElement, List`1& projects, SdkResult& sdkResult, Boolean throwOnFileNotExistsError)
   at Microsoft.Build.Evaluation.Evaluator`4.ExpandAndLoadImports(String directoryOfImportingFile, ProjectImportElement importElement, SdkResult& sdkResult)
   at Microsoft.Build.Evaluation.Evaluator`4.EvaluateImportElement(String directoryOfImportingFile, ProjectImportElement importElement)
   at Microsoft.Build.Evaluation.Evaluator`4.PerformDepthFirstPass(ProjectRootElement currentProjectOrImport)
   at Microsoft.Build.Evaluation.Evaluator`4.Evaluate(ILoggingService loggingService, BuildEventContext buildEventContext)
   at Microsoft.Build.Evaluation.Project.ProjectImpl.Reevaluate(ILoggingService loggingServiceForEvaluation, ProjectLoadSettings loadSettings, EvaluationContext evaluationContext)
   at Microsoft.Build.Evaluation.Project.ProjectImpl.ReevaluateIfNecessary(ILoggingService loggingServiceForEvaluation, ProjectLoadSettings loadSettings, EvaluationContext evaluationContext)
   at Microsoft.Build.Evaluation.Project.ProjectImpl.ReevaluateIfNecessary(EvaluationContext evaluationContext)
   at Microsoft.Build.Evaluation.Project.ProjectImpl.Initialize(IDictionary`2 globalProperties, String toolsVersion, String subToolsetVersion, ProjectLoadSettings loadSettings, EvaluationContext evaluationContext)
   at Microsoft.Build.Evaluation.Project..ctor(String projectFile, IDictionary`2 globalProperties, String toolsVersion, String subToolsetVersion, ProjectCollection projectCollection, ProjectLoadSettings loadSettings, EvaluationContext evaluationContext)
   at Microsoft.Build.Evaluation.ProjectCollection.LoadProject(String fileName, IDictionary`2 globalProperties, String toolsVersion)
   at OmniSharp.MSBuild.ProjectLoader.EvaluateProjectFileCore(String filePath, IReadOnlyDictionary`2 projectConfigurationsInSolution) in D:\a\1\s\src\OmniSharp.MSBuild\ProjectLoader.cs:line 157
   at OmniSharp.MSBuild.ProjectLoader.BuildProject(String filePath, IReadOnlyDictionary`2 configurationsInSolution) in D:\a\1\s\src\OmniSharp.MSBuild\ProjectLoader.cs:line 75
   at OmniSharp.MSBuild.ProjectFile.ProjectFileInfo.Load(String filePath, ProjectIdInfo projectIdInfo, ProjectLoader loader, Guid sessionId, DotNetInfo dotNetInfo) in D:\a\1\s\src\OmniSharp.MSBuild\ProjectFile\ProjectFileInfo.cs:line 116
   at OmniSharp.MSBuild.ProjectManager.<>c__DisplayClass31_0.<LoadProject>b__0() in D:\a\1\s\src\OmniSharp.MSBuild\ProjectManager.cs:line 302
   at OmniSharp.MSBuild.ProjectManager.LoadOrReloadProject(String projectFilePath, Func`1 loader) in D:\a\1\s\src\OmniSharp.MSBuild\ProjectManager.cs:line 313

[fail]: OmniSharp.MSBuild.ProjectManager
        Attempted to update project that is not loaded: c:\Projects\i21RESTfulApi\i21RESTfulApi.csproj

Steps to reproduce

Install .NET 5.0 SDK and Hosting Bundle

Expected behavior

It should load the project/solution

Actual behavior

Unable to load the project. Intellisense is not working. Formatting is not working. Parsing and error highlighting is not working.

[filipw]

the problem is here

1: Visual Studio Community 2019 16.7.30611.23 - “C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Current\Bin”

Omnisharp sees that you have Visual Studio installed on your machine and tries to use its MSBuild.

However your Visual Studio installation is not up to date - 16.8 is the lowest version needed to work with .NET 5.0.

You need to update your Visual Studio or uninstall it.

[covamalia]

“Update Visual Studio” may not always be the best suggestion. There could be situations where this is not possible (for example Visual Studio extension incompatibility or company internal IT procedures) and so updating may not always be quite as straight forward for some as it is for others. Also, an update to Visual Studio is a larger undertaking, so if someone runs into the issue when trying out a quick prototype, then the ease of usability is lost.

If Omnisharp is being told to use “latest”, then you would expect it to always pick up the latest version of MSBuild. Out of the two options of 16.7.30611.23 and 16.8.0 then you would expect this would pull out the second one (which is also the one that Omnisharp will happily grab an update for by itself).