ViewState error with dynamically built menu

I have a Menu control that I dynamically populate with categories. When a user clicks a category, the postback should populate a grid with products in that category. However, I seem to have tried every way possible, i.e. whatever page life cycle time, only to always get this error:

Failed to load viewstate. The control tree into which viewstate is being loaded must match the control tree that was used to save viewstate during the previous request.

Here is all my code:

protected void Pag开发者_JAVA百科e_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        BuildCategoryMenu();
    }
}

protected void categoryMenu_ItemClick(object source, DevExpress.Web.ASPxMenu.MenuItemEventArgs e)
{
    var catId = new Guid(e.Item.Name);
    ListProductsByCatId(catId);
}

private void BuildCategoryMenu()
{
    var cats = _categoryService.ListActive();
    categoryMenu.Items.Clear();
    foreach (var cat in cats)
    {
        categoryMenu.Items.Add(new MenuItem { Text = cat.Name, Value = cat.id.ToString() });
    }
}

private void ListProductsByCatId(Guid catId)
{
    productGrid.DataSource = _productService.ListByCatId(new Guid("a5c2f0ef-a3cc-4af1-abac-37f1be6a5c74"));
    productGrid.DataBind();
}

Here is my Menu:

<asp:Menu ID="categoryMenu" runat="server" EnableViewState="false">
</asp:Menu>

EnableViewState is only false because it didn't work with true either.

---

One answer to this is to avoid the postbacks and code URL's into the menu items. More RESTful, but probably making AJAXing the menu a bit harder.