Preselection in a DropDownList

I'm just starting with MVC3 and I have the following situation.

My app's initial sign up page among other controls contains a drop down menu. When the user has completed the form then the form details are saved in a session and they move on to the next step. They may also move back to the original step to re-edit, in which case I need to show the drop down menu with the appropriate value preselected.

My code is as follows:

Controller:
public ActionResult Index()
{
   var model = new CompanyDetailsModel();
   BindDropDownLists(model);
   //IF WE HAVE A SESSION THEN PREFILL THE VALUES
   if(MySession.Current.IFA!=null)
   model = EditIFAProfileService.returnCompanyDetailSession(MySession.Current.IFA);
   return View("CreateCompanyDetails", model);
}

I am getting the expected values from the model, so for example the 
value model.Salutation is equal to an integer.

So, armed with that value I would expect to be able to set the preselected value of my dropdownlist as follows:

@Html.DropDownListFor(model => model.SalutationValue, Model.SalutationItems, 
"开发者_JS百科Please Select", new { @tabindex = "1" })

If I do set the model value of SalutationValue to an int then I get an error stating that

ViewData item that has the key is of type 'System.Int32' but must be of type 'IEnumerable'.

Any help would be much appreciated. Thank you.

---

Don't use any ViewData if you are working with strongly typed views and view models as it would conflict. Simply set the SalutationValue property to some given value. Here's an example:

public ActionResult Index()
{
    var model = new CompanyDetailsModel();
    model.SalutationItems = ...
    if (MySession.Current.IFA != null)
    {
        model.SalutationValue = MySession.Current.IFA;
    }
    return View("CreateCompanyDetails", model);
}