Quick fix for MSB4018 The RazorTagHelper task failed unexpectedly.

 After upgrading to Visual studio 16.8.0 some of your projects depending on Netstandard 2.0 may not build due to Razor Tag Helper task failing.

The Output Window will show a message containing the following:-

MSB4018 The RazorTagHelper task failed unexpectedly. 

The Fix

1. Install 3.1 SDK of .NET Core. Can be located from the following link:- https://dotnet.microsoft.com/download/dotnet-core/3.1
2. Add global.json file to your visual studio project and add the following to it to pin the project to 3.1 SDK:-

    {

          "sdk": {

                    "version": "3.1.403"

                      }

    }

To Reproduce

Open an existing .NET Core 2.2 app in VS 16.8.0

Build the project.

The Error will be displayed in the Error window and the project cannot be run.