ASP.NET Session Expires while viewing server reports

[Frank]

Hi,
We have a web application which is using SQL reports(2005). The Web
application and Reports (server reports) exist in the same machine.
When we try to view the report through report viewer from the
application, Sometimes we get "ASP.NET Session Expired" message. But
when i click the same report link again, the report is getting loaded.
This error is not coming everytime & not specific for any particular
report.
I will be really greatful if someone can assist us with a solution.
Thanks in advance