Null Exception in Session Values ?

Hi Friends,

I'm facing Session values goes to Null while using it. I have checked up the Session timing in  IIS, Webconfig, Everything has above 1 hour.  But i don't know, why my session values goes null when redirecting, Button Event Click etc.

My server OS : Windows server 2003.
IIS               : 6.

Please Help me to sort this issue.

Thanks in advance.