Sessions expires for the first time itself

[Guest]

Hi,
I'm running an ASP.net application where i'm using session variables.
The mode is 'InProc' and timeout is 30 mins
<sessionState mode="InProc" timeout="30"/>.

The application is working fine on DEV machine.
When uploaded into INT, whenever i'm running the application for the first
time i'm getting error 'Session expired'.
But if i goto the home page again and start running it, it's running fine.
More detail:
Page1 is my homepage where i'm stroing some data in session variable. After
clicking submit button it will redirect to Page2.aspx.
Page2 : load event i'm checking
if session is not nothing
do something here
else
redirect to error page saying that session expired.

Why my session is getting expired in INT?

Thanks