Forms Authentication, timing out in less than timeout period.

Hi I have forms authentication set up for a VB.Net 4.5 application with both the forms timeout and the sessionState timeout set to 20 minutes. It works fine on my development machine. However on the Shared hosted server(Not a web farm), user is redirected to login page in less than 20 minutes of inactivity. What am I missing?
Below is my web.config: As you can see, I have a tried to set the machineKey tag as well, but the issue remains.
<?xml version="1.0" encoding="utf-8"?> <configuration> <system.webServer> <directoryBrowse enabled="false" /> <modules> <remove name="FormsAuthenticationModule" /> <add name="FormsAuthenticationModule" type="System.Web.Security.FormsAuthenticationModule" /> <remove name="UrlAuthorization" /> <add name="UrlAuthorization&q ...