checked chaged event is not firing within update panel

With very limited information that you have provided, hope you have added the following in your code :

- You might be using AJAX in your ASP.NET application, so make sure you have added ScriptManager in the .aspx file.

- Add Triggers to your UpdatePanel for each control like this :

<asp:UpdatePanel ID="myPanel" runat="Server" xmlns:asp="#unknown">
<contenttemplate>
 <!-- Declare your controls here -->
</contenttemplate>
<triggers>
 <asp:AsyncPostBackTrigger ControlID="giveYourControlID" EventName="Checked" />
</triggers>

With this your event handling will be taken care of.
Hope it helped!