Installation error by NuGet VS2015

I tried to install it on NuGet, but with error:

Could not install package 'NeuralNetwork.NET 2.1.3'. You are trying to install this package into a project that targets '.NETFramework,Version=v4.6.1', but the package does not contain any assembly references or content files that are compatible with that framework. 

could anyone help me ?

thanks

