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

C:Program Filesdotnetsdk2.1.4SdksMicrosoft.NET.SdkuildMicrosoft.NET.TargetFrameworkInference.targets(135,5): error : The current .NET SDK does not support targeting .NET Core 2.1.  Either target .NET Core 2.0 or lower, or use a version of the .NET SDK that supports .NET Core 2.1. [E:GitHubKerryJiangSuperSocket estTestTest.csproj]

https://stackoverflow.com/questions/46829923/the-current-net-sdk-does-not-support-targeting-net-core-2-0

If your platform target is 32bit, then you have to install x86 installation of the sdk.