Forms Authentication timing out when it shouldn't?

Question

I have a problem with an ASP.NET application that is driving me nuts.

When a user leaves a page inactive for a period of time the session was timing out and error were b

Answer 1

Thanks for the response guys: I have already explicitly set slidingExpiration to true in the web.config with no effect.

The timeout values are: Session: 20 minutes FormsAuthentication: 60 minutes

I have left the session timeout as is and reduced the FormsAuthentication to 12 minutes for testing. The defrib 'pings' every 10 minutes. If I leave the page inactive for 14 minutes and then click a button I get the problem #edit: but not everytime it seems!#.