I know this question already has an accepted answer, but for me, a .NET beginner, there was a simple solution to what I was doing wrong and I thought I’d share.
I had been doing this:
@Html.HiddenFor(Model.Foo.Bar.ID)
What worked for me was changing to this:
@Html.HiddenFor(m => m.Foo.Bar.ID)
(where “m” is an arbitrary string to represent the model object)