title: Multiple controls with the same ID were found
body: <p>I have following asp.net code but it gives error when I change dropdown selected index:</p>
  
  <pre><code>&lt;asp:UpdatePanel&gt;
        &lt;ContentTemplate&gt;
          &lt;asp:DropDownList ID="drp" runat="server" AutoPostBack="true" OnSelectedIndexChanged="drp_SelectedIndexChanged"&gt;
            &lt;asp:ListItem Text="ABC" Value="ABC"&gt;&lt;/asp:ListItem&gt;
            &lt;asp:ListItem Text="DEF" Value="DEF"&gt;&lt;/asp:ListItem&gt;
          &lt;/asp:DropDownList&gt;
          &lt;asp:Panel ID="pnl" runat="server"&gt;
          &lt;/asp:Panel&gt;
          &lt;asp:Button ID="Button1" runat="server" Text="Submit" OnClick="Button1_Click" /&gt;
        &lt;/ContentTemplate&gt;
        &lt;Triggers&gt;
          &lt;asp:PostBackTrigger ControlID="drp" /&gt;
          &lt;asp:PostBackTrigger ControlID="Button1" /&gt;
        &lt;/Triggers&gt;
      &lt;/asp:UpdatePanel&gt;
  </code></pre>
  
  <p>Now made one function for create textbox and get textbox value into lable as following way</p>
  
  <pre><code>protected void drp_SelectedIndexChanged(object sender, EventArgs e)
  
  {
    if (drp.SelectedIndex != 0)
    {
      ViewState["controls"] = true;
      CreateTextbox(drp.SelectedIndex);
    }
  
  }
  
  private void CreateTextbox(int Number)
  {
    try
    {
      TextBox txtTextbox;
      Label lbltxtTextbox;
      for (int i = 0; i &lt; Number; i++)
      {
        txtTextbox = new TextBox();
        txtTextbox.ID = "txtbox" + i;
        lbltxtTextbox = new Label();
        lbltxtTextbox.ID = "lbltxtbox" + i;
        pnl.Controls.Add(txtTextbox);
        pnl.Controls.Add(lbltxtTextbox);
      }
    }
    catch (Exception ex)
    {
    }
  }
  
  private void GetTextboxvalue(int Number)
  {
    try
    {
      TextBox txtTextbox;
      Label lbltxtTextbox;
      for (int i = 0; i &lt; Number; i++)
      {
        txtTextbox = (TextBox)pnl.FindControl("txtbox" + i);
        lbltxtTextbox = (Label)pnl.FindControl("lbltxtbox" + i);
        lbltxtTextbox.Text = txtTextbox.Text;
      }
    }
    catch (Exception ex)
    {
    }
  }
  
  protected void Button1_Click(object sender, EventArgs e)
  {
    GetTextboxvalue(drp.SelectedIndex);
  }
  protected void Page_Load(object sender, EventArgs e)
  {
  
    if (ViewState["controls"] != null)
      if (drp.SelectedIndex != 0)
      {
        CreateTextbox(drp.SelectedIndex);
      }
  
  
  
  }
  </code></pre>
  
  <p>error is:</p>
  
  <pre><code>Multiple controls with the same ID 'txtbox0' were found. FindControl requires that controls have unique IDs.
  </code></pre>