So I have a page, say just has one button generated like this,

 using (Html.BeginUmbracoForm("GoAddPerson", "PersonSurface", null, new { name = "myForm" })) 

        {
          <input type="submit"/>
        }

This then calls a controller method which aims to return a new view

 [ValidateInput(false)]
    [HttpPost]
    public ActionResult GoAddPerson()
    {

        var m = new myproj.Models.PersonAddModel();
        return View("~/Views/PersonAdd.cshtml", m); 


    }

But when tried, it just throws the Exception in the subject line .. If I make my model inherit from RenderModel then it works fine, and that is what I usually do, however I understand it doesn't have to inherit from RenderModel and in this case it is not useful to .. so just wonder what I am doing wrong here, and why the exception?

Thanks in advance for any help