Package Microsoft.CSharp 4.5.0compatible with netcoreapp2.1 Error Message

I am trying to run a ASP.NET Core 2.0 app. However when I click on run in IDE (to build the app) I get this error:

Controller.csproj: [NU1202] Package Microsoft.CSharp 4.5.0 is not compatible with netcoreapp2.1 (.NETCoreApp,Version=v2.1). Package Microsoft.CSharp 4.5.0 does not support any target frameworks.

Controller.csproj: [NU1202] Package System.Security.Principal 4.3.0 is not compatible with netcoreapp2.1 (.NETCoreApp,Version=v2.1). Package System.Security.Principal 4.3.0 does not support any target frameworks.

Thank you inadvance.