ASP.NET Forms Authentication expiring even with activity

I have a ASP.NET MVC site which uses ASP.NET Formsauthentication I have the ticket set to expire after 20 minutes of inactivity. However it is expiring after 20 minutes no matter what.

I gue开发者_运维技巧ss what I am asking is, is this the right functionality of it or do I have some issue and if so a solution to this would be appreciated.

Verify the following

1) slidingExpiration = true 2) The login is not being dropped after an app recycle. 3) Also setting the machineKey explicitly in your web.config if you are in a shared environment