Session Timeout even set the value in web.config on postback

Question

I have a web application in which i have locations they are cascade in nature just like that 

Country------>city-------->state------>regions

 

 

they are populating based on the values of each other just like when i select the country its cities are populated and when i select the city its states populates and when i select the state its region populates

just like the below interface

due to post back because on selected_index changes on checkboxList of Country i populates Cities chckbox list so on post back its loggout whet would be the fix, thanks in advance .

 

Regards

Mark