New session starts when I click on a link in my asp.net website

Hi all,
For some reason, a new session gets started whenever I click a link on my asp.net website. And so,  al session stored values are also lost from one page to the other.
The link markup is like this in my .aspx file:

<a href="manage_menu.aspx">
I do a Response.Write(Session.SessionID) on both this page and manage_menu.aspx and both print different text.
My asp.net website is targeting .net framework 4.5 and the session part of web.config looks like this:

<sessionState mode="InProc" customProvider="DefaultSessionProvider"> <providers> <add name="DefaultSessionProvider" type="System.Web.Providers.DefaultSessionStateProvider, System.Web.Providers, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" connectionStringName="DefaultConnection" /&g ...