Package restore failed when I use a portable library

I am trying to install the nuget pacakge EntityFramwork.Sqlite in a portable library which targets are .net 4.6 and windows universal 10.0. If I do that, I get an error that says package restore failed.

If I create project library that is for .net 4.6 then I can add the package and if I create a universal portable library only for windows 10 applications, I can add the package too.

So, if I can use the package in .net 4.6 projects and windows universal projects, why can I not use it in a portable library that targets this kind of projects?

Thanks.