Forms authentication ticket expired before the session timeout

Hi,
We are having a problem with sessions randomly timing out in Visual Studio 2005 or .NET 2.0 (well seemingly randomly) and couldn't find the problem. Later we found that the authentication ticket is expired well before the session timeout.
Our code in Web.config is as follows 
<forms name="ASPXAuth" loginUrl="login.aspx" protection="All" timeout="45" path="/" slidingExpiration="true"> </forms>

And in login.aspx, we are creating the Authentication ticket as follows.
//Initialize FormsAuthentication
FormsAuthentication.Initialize();//Generate a new ticket used for authentication ...