Ajax BeginForm not calling action in controller - ajax

Question

I have been trying to implement a system where a user can add/delete child entities of the current entity, however I have been having trouble using the Ajax.BeginForm helper method (this is my first real use of it). Basically when I click the submit button, it won't call the specified action in my controller.
I have searched for several hours now without success, most of the issues people have had before is due to certain libraries not being referenced, but I'm pretty sure that's not the issue here.
Anyway, here are the important parts of my code:
Partial View
#using MyProject.Domain.Entities;
#model MyProject.WebUI.ViewModels.UserCustomerViewModel
<div id = "meh222">
#using (
Ajax.BeginForm("AddCustomer", "User",
new AjaxOptions() { UpdateTargetId = "meh222", HttpMethod = "Post" })
)
{
<label>Customers</label>
#*#Ajax.ActionLink("Add Customer", "AddCustomer", "User", new { userID = Model.UserID, customerID = 1001 },
new AjaxOptions() { UpdateTargetId = "meh222", HttpMethod = "POST" }, new { #class = "standardbutton" })*#
<fieldset>
<legend>CustomersLegend</legend>
#Html.HiddenFor(m => m.UserID)
#Html.DropDownListFor(m => m.Customers, new SelectList(Model.AllCustomers, "CustomerID", "Name"))
<p>
<input type="submit" value="Add Customer" />
</p>
</fieldset>
}
<table class="tbl2" id="tbl2">
<thead>
<tr>
<th>CustomerID</th> <th>Name</th> <th>Actions</th>
</tr>
</thead>
<tbody>
#if (Model != null)
{
foreach (Customer item in Model.Customers)
{
<tr>
<td>
#Html.DisplayTextFor(i => item.CustomerID)
</td>
<td>
#Html.DisplayTextFor(i => item.Name)
</td>
<td>
#Ajax.ActionLink("Delete", "DeleteCustomer", "User", new { userID = Model.UserID, customerID = item.CustomerID },
new AjaxOptions() { UpdateTargetId = "meh222" }, new { #class = "standardbutton" })
</td>
</tr>
}
}
</tbody>
</table>
</div>
Main View
<div>
#{ Html.RenderPartial("CustomerPartial", Model.CustomerVM); }
</div>
Controller
[AcceptVerbs(HttpVerbs.Post)]
public PartialViewResult AddCustomer(UserCustomerViewModel vm)
{
return PartialView("CustomerPartial");
}
View Model
public class UserCustomerViewModel
{
public int UserID;
public IEnumerable<Customer> Customers { get; set; }
public IEnumerable<Customer> AllCustomers { get; set; }
}
Scripts in my _Layout
<script src="#Url.Content("~/Scripts/jquery-1.5.1.js")" type="text/javascript"></script>
<script src="#Url.Content("~/Scripts/jquery-1.5.1.min.js")" type="text/javascript"></script>
<script src="#Url.Content("~/Scripts/jquery-ui-1.8.11.js")" type="text/javascript"></script>
<script src="#Url.Content("~/Scripts/jquery-ui-1.8.11.min.js")" type="text/javascript"></script>
<script src="#Url.Content("~/Scripts/jquery.unobtrusive-ajax.js")" type="text/javascript"></script>
<script src="#Url.Content("~/Scripts/jquery.unobtrusive-ajax.min.js")" type="text/javascript"></script>
<script src="#Url.Content("~/Scripts/MicrosoftMvcAjax.js")" type="text/javascript"></script>
<script src="#Url.Content("~/Scripts/MicrosoftAjax.js")" type="text/javascript"></script>
<script src="#Url.Content("~/Scripts/modernizr-1.7.min.js")" type="text/javascript"></script>
Just a couple of notes:
If you look in my partial view, you can see an Ajax.ActionLink commented out. This was what I used before (and it worked), however I needed to hardcode the CustomerID, hence the change to Ajax.BeginForm so I can access the value of the DropDownList that is populated from the ViewModel's AllCustomers property.
The real controller action obviously has more processing, but that isn't the problem here as if I put a breakpoint in the action it isn't even hit.
I have added the list of scripts just so people know exactly what I am referencing in case that is the issue.
Does anyone have any ideas why my submit isn't accessing the AddCustomer action in my controller?
If I haven't decribed the issue properly or you need more information, please let me know and I will try and give more information.
Thanks very much.
----UPDATE----
Error data I got from Chrome's console
This is under the '500 Internal Server Error' in the console.
d.support.ajax.d.ajaxTransport.send jquery-1.5.1.min.js:19
d.extend.ajax jquery-1.5.1.min.js:19
e jquery.unobtrusive-ajax.min.js:5
(anonymous function) jquery.unobtrusive-ajax.min.js:5
E jquery-1.5.1.min.js:19
d.event.handle jquery-1.5.1.min.js:19
d.event.add.k.handle.m jquery-1.5.1.min.js:19