aspx page get hanged with update panel and timer

Question

my the help of "tick event" of timer i execute some functios.

My problem is, it only executes 1 time by the help of "timer tick" event

then it gets hanged !!!!!

I donot know where it goes???

I have debugged it to find or see the flow where it is going but not

get success yet

and when i use chrome browser after some time it gives me message your page get expired you want to wait or continue???

kindly help me out it would be so nice of youi am very much stuck kindly help me out

I am using update panel with ajax timer 
its my pusedocode

<asp:Timer ID="mytimer" runat="server" Interval="5000" OnLoad="mytimer_Load" OnTick="mytimer_Tick">

       </asp:Timer>

<asp:UpdatePanel ID="upPnl" runat="server">

           <Triggers>

               <asp:AsyncPostBackTrigger ControlID="mytimer" EventName="Tick" />

           </Triggers>

<ContentTemplate>

               <asp:TextBox ID="txt" runat="server" Width="300px"></asp:TextBox>

</ContentTemplate>

   </asp:UpdatePanel>

my the help of "tick event" of timer i execute some functios.

My problem is, it only executes 1 time by the help of "timer tick" event

then it gets hanged !!!!!

I donot know where it goes???

I have debugged it to find or see the flow where it is going but not

get success yet

and when i use chrome browser after some time it gives me message your page get expired you want to wait or continue???

kindly help me out it would be so nice of you