Fixed. The issue was with the model I was passing to the document type view from the controller.
In the Umbraco documentation it says, you can create a controller to hijack the Umbraco route and serve up your own view with a custom model, like so:
public ActionResult Index(RenderModel model)
{
SearchResultsViewModel viewModel = new SearchResultsViewModel
return CurrentTemplate(viewModel);
}
and in my view I had:
@inherits UmbracoViewPage<SearchResultsViewModel>
However, it seems as though, in order to do that, you must make sure your custom view model in inherits from RenderModel with a constructor that takes RenderModel as a parameter and then sets some properties on the base object, like so:
public class SearchResultsViewModel :RenderModel
{
public SearchResultsViewModel(RenderModel model) : base(model.Content, model.CurrentCulture)
{
}
}
Previously, my view model had not inherited from anything and had a parameterless constructor.
This article led me to the right answer.
http://www.ben-morris.com/using-umbraco-6-to-create-an-asp-net-mvc-4-web-applicatio
Also, as a side note, I still get the ReSharper warning of "Cannot resolve partial view PropertySearchResultDesktop" but I think that's a ReSharper bug rather than an error.
Even with a full path and file extension in the call, it still complains.
I do find it odd though that while debugging, even with my old controller code, no exception was thrown at the model binding stage or inside the controller, or in the view until it go to the Html.Partial call.
Anyway, I hope this helps anyone having the same issue.