How to use Client Script at .cs side when update panel is present on the page

Once I was trying to access client script at .cs side by using ClientScript.RegisterStartupScript. But somehow it didn't work.After doing some research I found the solution to it.I realised that the reason why it wasn't working was because of  update panel present on the page.

ClientScript.RegisterStartupScript(typeof(System.String), "message", 
"<script> alert('I'm unable to access it in Update Panel.');</script>");     

 <asp:ScriptManager ID="sManger" runat="server"  >
 </asp:ScriptManager>

ScriptManager.RegisterStartupScript(this, typeof(string),
 "message", "alert('It is working now.');", true);