The current .NET SDK does not support targeting .NET Core 2.1. Either target .NET Core 2.0 or lower, or use a .NET SDK that supports .NET Core 2.1

Question

have tried upgrading to the professional version of visual studio 2017 v 15.6.0 (Preview 7.0)

and installed aspnetcore-runtime-2.1.0-preview1-final-win-x64 and .net

Answer 1

https://www.microsoft.com/net/download/visual-studio-sdks

You can download the SDK from the above site

check the SDK which is in your machine Path C:\Program Files\dotnet\sdk

Change or check the target framework in visual studio,

Right click on Startup Application or project => Application => Target Framework.

You can change the framework and build the solution and restore nugget packages.