[Solved] Web Page expires when user is not active (Idle) for 5 Minutes after hosting

dear fiend

The first, thanks the friends in this forum has helped me a lot of to build the application website ASP.net C#.

At moment, I finish create  the webapp, but I'm facing a problem is when i open the web, in 5 minutes if I don't have any actions on page then click on any  link on  website, it will redirect to login page.

Why web pages expire when do not active in 5 minutes

i login to control panel and go to application pool and see that:

Idle timeout (minutes) 5

Amount of time a worker process will remain idle before it shuts down.

I can't edit the minutes, it read only.

my web.config:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <configSections />
  <appSettings />  
  <system.web>
    <httpRuntime executionTimeout="999999" />
    <compilation debug="true" targetFramework="4.5.2" />  
    <trust level="Full" />
    <authentication mode="Forms" />     
    <sessionState timeout="60"></sessionState>
    <customErrors mode="Off" defaultRedirect="" />
    <machineKey validationKey="308A5193B77D18BB33F286DCC941A54331AE8D000104EAC1DB843D98B1CB457AF9A813B4D5D7D77220987AC8EA478401577194FC20E6CCE8ACEC159C5C59D754" decryptionKey="46C25F7D8BFDE6DAF886AEC2706EFA6A2706C43C752B69C82D5B13A29EA246C1" validation="SHA1" decryption="AES" />
  </system.web>
  <system.webServer>
    <directoryBrowse enabled="true" />
        <defaultDocument>
            <files>
                <clear />
                <add value="default.aspx" />
                <add value="Default.htm" />
                <add value="Default.asp" />
                <add value="index.htm" />
                <add value="index.html" />
                <add value="iisstart.htm" />
            </files>
        </defaultDocument>
  </system.webServer>  
</configuration>

In my code I use masterpage (main.master) and session:

Login.cs

if user Login susscess:

HttpContext.Current.Session.Timeout = 60; 
HttpContext.Current.Session["UserName"] = txtUserName.Text;

In main.master i use:

<asp:ScriptManager id="toolScriptManageer1" runat="server" EnableHistory="true" EnablePartialRendering="false" EnablePageMethods="true"> </asp:ScriptManager>

and in Main.master.cs: 

        protected void Page_Load(object sender, EventArgs e)
        {
            if (HttpContext.Current.Session["UserName"] == null)
            {
                Response.Redirect("~/login.aspx");
                Context.ApplicationInstance.CompleteRequest();
            }
                        
            if (!IsPostBack)
            {               
                  DataTable dt = this.GetData(0);
                  PopulateMenu(dt, 0, null);               
            }
        }

Please help me