Session State

Hellooo...
I have a small problem with my application. I actually have a session which saves the username. But after some idle time, if i want to go back to the main menu, where the username actually appears, i have an error. The code on the Main menu is as follows:
 lblUsername.Text = Session("Username").ToString()
and on the login page it is as follows:
If dsUserInfo.Tables(0).Rows.Count > 0 Then status = True Session.Add("Username", dsUserInfo.Tables(0).Rows(0)("Username")) Else status = False
End If

Can anyone please help me to perhaps put a session timeout and a message displaying "Timeout. Please Login Again." And redirects the user to the login page upon clicking ok on the message.

Thanks
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