title: mvc form cannot create an abstract class
body: <p>I have a form with 2 select box. But when I click the submit button, there's an error saying "Cannot create an abstract class". I have no idea what is going wrong here</p>
  
  <pre><code>@using (Html.BeginForm("Add", "Admin")) { 
      &lt;input type="submit" value="Add" class="btn btn-warning small-text custom-btn" /&gt;
  
      &lt;div class="select-box"&gt;
          &lt;select name="users[]" multiple size="35"&gt;@{ Html.RenderAction("UserList", "GroupsAndUsers"); }&lt;/select&gt;
      &lt;/div&gt;
  
       &lt;div class="select-box"&gt; 
          &lt;p class="blue-text bold-text"&gt;Groups&lt;/p&gt;
          &lt;select name="group" size="35"&gt;@{ Html.RenderAction("GroupList", "GroupsAndUsers"); }&lt;/select&gt;
      &lt;/div&gt;
  
      &lt;input type="hidden" name="RedirectToUrl" value="~/GroupsAndUsers/AddUsers" /&gt;
  }
  </code></pre>
  
  <p>Admin/Add</p>
  
  <pre><code>[HttpPost]
          public ActionResult Add(Array userIDs, int groupID, string RedirectToUrl)
          {
  
              return Redirect(RedirectToUrl);
          }
  </code></pre>