How can I extend the Forms Authentication time in ASP.Net?

Question

When I post something on my ASP.Net website,
the sessions on page are become null if been waited 7 minute and 10 seconds.

I have this on Global.asax's onSessionStart method

Session.Timeout= 60;

And have this code in web.config but any of it does not work :

<system.web>
  <authentication mode="None">
    <forms timeout="30" slidingExpiration="true" />
  </authentication>

How can I fix this?

Answer 1

Are you sure the authentication is working, since it is set to none.

It should be set to Forms. ie

<authentication mode="Forms">

Answer 2

I found that this is belong to server's session idle time.
I have changed it in Application Pools.

To do this :
Control Panel/
Administrative Tools/
Internet Information Services (IIS) Manager/
on the left : Application Pools
right click and select Advanced Settings/
IIS Time-out...