Hi satya,
in web.config set like this working fine
<sessionState timeout="120"/>
otherwise
go through below url and download ASPNET_jQueryUI_Dialog_Timeout example try it
working fine
https://skydrive.live.com/?cid=f7c93b143c55f787&sc=documents&id=F7C93B143C55F787%21230#cid=F7C93B143C55F787&sc=documents[^]