I get the same problem in Visual Studio Ultimate 2012, although I installed the latest update and updated the NuGet Package Manager to the latest version 2.8.60318.667 in Visual Studio 2012. Then I will try to install this package in Visual Studio 2013, where the NuGet Package Manager version is 2.8 .60610.756. The SSH.NET package has been installed successfully.
So, I'm afraid there is a problem between the current version of the SSH.NET package and the NuGet package manager version 2.8.60318.667. But this problem was solved in Visual Studio 2013, I suggest you upgrade Visual Studio to a higher version.
Another way for your problem is to install the previous version of the SSH.NET package in Visual Studio 2012. I checked SSH.NET 2016.0.0-beta2 , it can install successful operation in Visual Studio 2012.
Weiwei Cai - MSFT
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