无法在Visual Studio中使用IronPython安装MahApps程序集（使用PTVS 2.0）

I am trying to create a MahApps styled WPF application using IronPython 2.7.3 in Visual Studio Ultimate 2012 with PTVS. However I cannot install MahApps.Metro via Nuget using the GUI. Choosing 'Install' in the Manage NuGet Packages console trows the following error by Visual Studio:I am trying to create a MahApps styled WPF appl