MVC :: File Not Passing To Controller?

I am getting an null referance on file, what am I doing wrong.

<% Html.EnableClientValidation(); %>
<% Html.BeginForm("AddMedia", "Pattern", new { id= Model.Pattern_Guid} , FormMethod.Post, new {enctype = "multipart/form-data"}); %>
<%: Html.ValidationSummary(true) %>
<%: Html.Label("height") %>
<%: Html.TextBox("height") %>
<%: Html.Label("width") %>
<%: Html.TextBox("width") %>
<%: Html.Label("Media") %>
<input type="file" id="Media" name="Media" />
<input type="submit" name="btnAdd" value="Add" />
<% Html.EndForm(); %>

controller code:

[HttpPost]
public ActionResult AddMedia(Guid id, HttpPostedFileBase file, FormCollection collection)
{
string mimeType = file.ContentType; // Null Exception here ....