I'm having this problem only when I target .Net 4.6 framework under both Visual Studio 2015 or 2013. There is no XML Documentation Comments
present in the Enumerable class
(System.Linq.Enumerable, \Reference Assemblies\Microsoft\Framework.NETFramework\v4.6\System.Core.dll). Anyone having the same problem?
I reinstalled .NET Framework 4.6 Targeting Pack (http://blogs.msdn.com/b/dotnet/p/dotnet_sdks.aspx) but that didn't solve the problem. It seems that System.Core.xml file in \ReferenceAssemblies\Microsoft\Framework.NETFramework\v4.6\ is missing some of the documentation. In the end I have used System.Core.xml file from .Net 4.5.2, and now documentation is visible.
Well it looks like they fixed this bug with the Update-1 for Visual Studio 2015. After installing update documentation is present!