Session Time out problem

Hi frns,

I am having some problem with expiration of session in my ASp.Net application.
The problem is that, my session is getting expired before the prespecified time duration in web.config file.I am not using page level session timeouts nor in global.asax.

I am using forms authentication. Both- auhentication timeout and session time out i hav specified as 20 in web.config file. I am just pasting that section frm my web.config file:

<authentication mode="Forms">
<forms loginUrl="index.aspx" timeout="20">
</forms>
</authentication>
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<sessionState
mode="InProc"
stateConnectionString="tcpip=127.0.0.1:42424"
sqlConnectionString="data source=127.0.0.1;Trusted_Connection=yes"
cookieless="false"
timeout="20"
/>



here session is timed outeven before 20 minutes.
Can anyone please help me with the reason and a solution for this strange problem i am facing?

Thanks in advance,

Sunil