For those of you suffering with this after migrating a project from VS 2013 to VS 2015, I was able to fix this issue by installing the ASP.NET tools update from https://visualstudiogallery.msdn.microsoft.com/c94a02e9-f2e9-4bad-a952-a63a967e3935/file/77371/6/AspNet5.ENU.RC1_Update1.exe?SRC=VSIDE&UPDATE=TRUE.