Not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression

I have looked at all the examples related to this but have not been able to solve my issue.

I am creating a dropdownlist in asp .net mvc3.

I have a repository which returns:

    public IEnumerable<SelectListItem> GetPropertyTypeSelectList()
    {
        var propertyTypes = from p in db.PropertyType
                                orderby p.PropertyTypeDescription
                                select new SelectListItem
                                {
                                    Text = p.PropertyTypeDescription,
                                    Value = p.PropertyTypeId.ToString()
                                };
        return propertyTypes;
    }

My viewmodel looks like this:

public class AddPropertyViewModel
{
    public Property Property { get; set; }
    public IEnumerable<SelectListItem> PropertyTypes { get; set; }
    public IEnumerable<SelectListItem> FurnishedTypes { get; set; }
}

My controller for "create" action for HttpGet looks like this:

    public ActionResult AddProperty()
    {
        AddPropertyViewModel viewModel = new AddPropertyViewModel
        {
            PropertyTypes = websiterepository.GetPropertyTypeSelectList()

        };
        return View(viewModel);
    }

and the view is like this:

    <div class="editor-label">
        @Html.LabelFor(model => model.Property.PropertyType)
        @Html.DropDownListFor(model => model.Property.PropertyType, Model.PropertyTypes)
    </div>

I am getting the error above. From what I have read it looks like ToString() is causing the problem. But I am not sure how to correct it.

Thanks.