The specified framework 'Microsoft.AspNetCore.App', version '2.1.0' was not found

Question

I tried to upgrade my web app from .net core 2.0 to .net core 2.1 I did:

1) Install Visual Studio Professional 2017 Preview Version 15.8.0 Preview 1.1
2) Installed the .net core 2.1.3 RC1 SDK from here: https://www.microsoft.com/net/download/dotnet-core/sdk-2.1.300-rc1
3) Updated all of my aspnetcore nuget packages to the latest version.

After doing both of these things, when I start my project I get this screen:

HTTP Error 502.5 - Process Failure Common causes of this issue:

The application process failed to start
The application process started but then stopped
The application process started but failed to listen on the configured port 

Troubleshooting steps:

Check the system event log for error messages
Enable logging the application process' stdout messages
Attach a debugger to the application process and inspect 

For more information visit: https://go.microsoft.com/fwlink/?LinkID=808681

and in my Output window from ASP.NET Core Web Server, I get this:

The specified framework 'Microsoft.AspNetCore.App', version '2.1.0' was not found.
  - Check application dependencies and target a framework version installed at:
      C:\Program Files\dotnet\
  - Installing .NET Core prerequisites might help resolve this problem:
      http://go.microsoft.com/fwlink/?LinkID=798306&clcid=0x409
  - The .NET Core framework and SDK can be installed from:
      https://aka.ms/dotnet-download
  - The following versions are installed:
      2.1.0-preview2-final at [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
      2.1.0-rc1-final at [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
It was not possible to find any compatible framework version
The specified framework 'Microsoft.AspNetCore.App', version '2.1.0' was not found.
  - Check application dependencies and target a framework version installed at:
      C:\Program Files\dotnet\
  - Installing .NET Core prerequisites might help resolve this problem:
      http://go.microsoft.com/fwlink/?LinkID=798306&clcid=0x409
  - The .NET Core framework and SDK can be installed from:
      https://aka.ms/dotnet-download
  - The following versions are installed:
      2.1.0-preview2-final at [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
      2.1.0-rc1-final at [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]

Answer 1

.NET Core 2.1 SDK will be released this week. If you can't wait until then, add this to your *.csproj

<Project Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <TargetFramework>netcoreapp2.1</TargetFramework>
    <RestoreAdditionalProjectSources>
        https://dotnetfeed.blob.core.windows.net/orchestrated-release-2-1/20180515-07/final/index.json
    </RestoreAdditionalProjectSources>
  </PropertyGroup>
  
  ....
</Project>

And download the final SDK from: https://dotnetcli.blob.core.windows.net/dotnet/Sdk/2.1.300/dotnet-sdk-2.1.300-win-x64.exe

For more details visit: https://github.com/aspnet/Home/wiki/2.1.0-Early-Access-Downloads