I have an MVC2 Application that uses MVVM pattern. I am trying use Data Annotations to validate form input.

In my ThingsController I have two methods:

    [HttpGet]
    public ActionResult Index()
    {
        return View();
    }

    public ActionResult Details(ThingsViewModel tvm)
    {
    if (!ModelState.IsValid) return View(tvm);

        try
        {
Query q = new Query(tvm.Query);
            ThingRepository repository = new ThingRepository(q);

tvm.Airplanes = repository.All();                
return View(tvm);
        }
        catch (Exception)
        {
            return View();
        }
    }

My Details.aspx view is strongly typed to the ThingsViewModel:

<%@ Page Title="" 
         Language="C#" 
         MasterPageFile="~/Views/Shared/Site.Master"        
         Inherits="System.Web.Mvc.ViewPage<Config.Web.Models.ThingsViewModel>" %>

The ViewModel is a class consisting of a IList of returned Thing objects and the Query string (which is submitted on the form) and has the Required data annotation:

public class ThingsViewModel
{
    public IList<Thing> Things{ get; set; }

[Required(ErrorMessage="You must enter a query")] public string Query { get; set; } }

When I run this, and click the submit button on the form without entering a value I get a YSOD with the following error:

The model item passed into the dictionary is of type 
'Config.Web.Models.ThingsViewModel', but this dictionary 
requires a model item of type 
System.Collections.Generic.IEnumerable`1[Config.Domain.Entities.Thing]'.

How can I get Data Annotations to work with a ViewModel? I cannot see what I'm missing or where I'm going wrong - the VM was working just fine before I started mucking around with validation.