title: CheckBoxlist Updating a dropdowlist in UpdatePanel no longer PostBack
body: <p>I need to Update a Dropdowlist according to the selected value(s) in a CheckBoxList avoiding the page to reload, I am using an UpdatePanel.
  The dropdwonlist should always have an AutoPostback, it should always trigger my "SearchEvent"</p>
  
  <p>I used an UpdatePanel and an AsyncPostBackTrigger on my CheckBoxlist to call the function in code behind to refresh the dropdowlist.</p>
  
  <p>It works only one time. After the first call, I cannot trigger the CheckBoxlist SelectedIndexChanged, instead I get the error :</p>
  
  <p>"Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server. The status code returned from the server was: 404"</p>
  
  <p>My dropdownlist also lose the PostBack, nothing happens.</p>
  
  <p>The View ASPX :</p>
  
  <pre><code>&lt;td&gt;
  &lt;asp:ScriptManager ID="ScriptManager" runat="server" /&gt;
   &lt;asp:CheckBoxList ID="IsActiveFilterCheck" runat="server" AutoPostBack="true" AppendDataBoundItems="true" CausesValidation="False"&gt;
              &lt;asp:ListItem Text="Active" Value="1" /&gt;
              &lt;asp:ListItem Text="Closed" Value="0" /&gt;
   &lt;/asp:CheckBoxList&gt;
  &lt;/td&gt;
  &lt;td&gt;
  &lt;asp:UpdatePanel ID="UpdatePanel1" ChildrenAsTriggers="true" UpdateMode="Conditional" runat="server"&gt;
       &lt;Triggers&gt;
           &lt;asp:AsyncPostBackTrigger ControlID="IsActiveFilterCheck" EventName="SelectedIndexChanged" /&gt;
       &lt;/Triggers&gt;
      &lt;ContentTemplate&gt;
          &lt;br /&gt;&lt;br /&gt;
          &lt;asp:DropDownList ID="StatusFilterList" runat="server" DataTextField="Name" DataValueField="Id"&gt;
          &lt;/asp:DropDownList&gt;
     &lt;/ContentTemplate&gt;
  &lt;/asp:UpdatePanel&gt;
  &lt;/td&gt;
  </code></pre>
  
  <p>My code behind :</p>
  
  <pre><code>private void Page_Load(object sender, System.EventArgs e)
  {
  RegisterCallbacks();
  if (!IsPostBack)
  {
      Initialize();
       }
   }
  
   override protected void OnInit(EventArgs e)
  {
  // CODEGEN: This call is required by the ASP.NET Web Form Designer.
  CheckProfil();
  InitializeComponent();
  base.OnInit(e);
   }
  
  private void InitializeComponent()
  {
     this.SearchButton.ServerClick += new System.EventHandler(this.SearchButton_ServerClick);
     this.StatusFilterList.SelectedIndexChanged += new System.EventHandler(this.SearchButton_ServerClick);
     this.IsActiveFilterCheck.SelectedIndexChanged += new System.EventHandler(this.IsActiveFilterCheck_Changed);
     this.Load += new System.EventHandler(this.Page_Load);
  }
  
  protected void IsActiveFilterCheck_Changed(object sender, EventArgs e)
      {
          // Update the Status Filter List
          StatusFilterList.Items.Clear();
          if (IsActiveFilterCheck.Items.Cast&lt;ListItem&gt;().Where(li =&gt; li.Selected).ToList().Count != 1)
          {
              BindListInsertAll(StatusFilterList, ExpectedStatusCollection.Instance.GetAll());
          }
          else
          {
              IList statusSelected = ExpectedStatusCollection.Instance
                                                              .GetAll().Cast&lt;ExpectedStatusDo&gt;()
                                                              .Where(exp =&gt; IsActiveFilterCheck.SelectedValue == "1" ? exp.Id != 5 &amp;&amp; exp.Id != 6 : exp.Id == 5 || exp.Id == 6)
                                                              .ToList(); // Only Dead and Signed
              // Update the Status
              BindListInsertAll(StatusFilterList, statusSelected);
          }
  
          UpdatePanel1.Update();
          //FindByFilter();
      }
  </code></pre>
  
  <p>When I change the <em>IsActiveFilterCheck</em> checkboxlist I should update only the <em>StatusFilterList</em> as shown in the function <em>IsActiveFilterCheck_Changed</em>, without reloading the full page.</p>
  
  <p>This <em>StatusFilterList</em> should always be able to call/Trigger the event <em>SearchButton_ServerClick</em>  </p>
  
  <p>Right now It works only one time when the <em>IsActiveFilterCheck</em> is fired my dropdowlist is updated but after when I click anywhere I get the error and I can't trigger the <em>IsActiveFilterCheck</em></p>