Forms authentication in WebServices and timeout

[j_a5]

Hi,
I am having an issue with forms authentication and timeout. I created a
simple web application and a web service based on the example in
http://www.dotnetbips.com/displayarticle.aspx?id=166
I enabled the forms authentication for the web service and set the timeout
for the forms authentication to a small number (2 minutes). I am able to use
forms authentication to login to the webservice. However once I login, it
timesout at 2 minutes after I login even when I was accessing the web
service every 30 seconds. Is there something I am missing in forms
authentication and WebServices?
To reproduce
1. Create a simple app based on the example at
http://www.dotnetbips.com/displayarticle.aspx?id=166
2. Set the forms auth timeout to a small number say 2 min
3. log on and access the webservice every 30 seconds
4. After 2 minutes from logging in the webservice rejects the cookie
although you have been actively using it.

Thanks in advance
j_a5