DLL updates and sessions

[Amit Marathe]

I am using forms authentication and an in-proc session
state in my application. I noticed that updating a dll in
the bin directory while a session is in progress gives
rise to an error. i.e. the scenario is as follows:
1. user goes to page A which has a link to page B
2. a dll is updated after page A has rendered but before
the link to page B is clicked
3. the link to page B is followed

I am accessing the Session property of the Page object in
page B's OnLoad event and in the above sequence of events
I get an "Object reference not set to an instance" error.

It's OK that the old session is abandoned when I update
the dll but why does ASPX throw this error (rather than
starting a new session)?

Thanks.
Amit