We have enabled the ASP.NET Session State Service on all web servers. This will allow for sessions to be held by the service rather than the website worker process so sessions are not lost.
To enhance uptime and maintain a stable system we constantly recycle website application pools when they have either been inactive for too long or have received a specific number of requests.

As a result session state information can be lost.

The advantage of this new service is that sessions will not be destroyed if the worker process is recycled.

To take advantage of this service you need to edit your applications web.config file

You need to specify:

<sessionState mode="StateServer" />

Sites using ASP.Net v1.1 now have session state enabled by default.

Therefore if you use classic ASP v3 you can rename your .asp to .aspx to take advantage of sessionstate.