Error at publishing self-contained Core 2.0 application

Hi,

after creating a new asp.net core 2.0 application with vs 2017 (version 15.3.3) and trying to publish this application with

"dotnet publish -o dist -r netcoreapp2.0 -c Release"

I get the following error:

"C:\Program Files\dotnet\sdk\NuGetFallbackFolder\microsoft.netcore.app\2.0.0\build\netcoreapp2.0\Microsoft.NETCore.App.targets(19,5): error : Project is targeting runtime 'netcoreapp2.0' but did not resolve any runtime-specific packages for the 'Microsoft.NETCore.App' package.  This runtime may not be supported by .NET Core."

What can I do??