Prevent Auto logout in ASP.NET in all Browser specially Chrome

We need very little help and that is, We wants to prevent auto-logout in ASP.NET 3 tier web application, We have tried to use session timeout and other solutions but not able to prevent auto-logout in any where, <[login to view URL]> <authentication mode="Forms"> <forms timeout="99999999"/> </authentication> <sessionState timeout="999999" /> <[login to view URL]> We have tried above solution but not able to prevent auto-logout, Selected freelancer must able to prevent this, After he implement solution, We will wait for few hours before closing project. Freelancer must need to work remotely. Budget Fixed :- 600INR Timeframe :- 15 minute