Is my security cookie timing out?

[Paul W]

Hi - I have an app that does not use sessions:

<sessionState mode="Off" stateConnectionString="tcpip=127.0.0.1:42424"
sqlConnectionString="data source=127.0.0.1;Trusted_Connection=yes"
cookieless="true" timeout="600" />

It does use Forms authentication:

<authentication mode="Forms" >
<forms loginUrl="Login.aspx"
name = "Tenni" path="/"
protection="Validation" timeout="600" slidingExpiration="true">
</forms>
</authentication>


If a user leaves a session idle for a while (15 mins+) then when they go
back to it, it will redirect them to Login.aspx. The url for the displayed
page is then "blah.com\login.asp?RedirectUrl=nextpage.aspx" where
'nextpage.aspx' is the page they WANTED to move to.

I am no expert, but this appears to me that my security cookie is timing
out. I thought my settings in web.config (above) would prevent this.

In my call to System.Web.Security.FormsAuthentication.SetAuthCookie I have
tried specifying both a session and non-session cookie - but I get the same
problem.

Can someone shed any light, or suggest how I might get more info on what's
going on?

The problem only seems to occur on my production server (hosted at
www.discountasp.net). If I run it hosted on my own development machine, it
never does this(!).

Thanks,

Paul.