Users not logged out when session expires - ASP.NET - C#

[dihola]

Hi,
I have a problem with an ASP.NET C# application. When the session expires and then the user tries to access any page in the browser, instead of being transferred to the login page the website simply creates a new session and resumes the browsing as if nothing happened. I am using forms authentication and InProc sessions:

<authentication mode="Forms">
<forms name=".CRM" loginUrl="~/Login.aspx" defaultUrl="~/Default.aspx" cookieless="AutoDetect" domain=""/>
</authentication>

Any idea why is this happening?

Thanks very much