I know that this is a common issue but i try all and still with the problem of lost data session.

 There are all the thing i try:

• increase session time-out for the webserver
  
  • Open the properties for your DNN site in your IIS manager
  • Go to the tab "Home Directory"
  • Click the button "Configuration" in the lower section of the screen
    (You now have a window named "Application Configuration")
  • Go to the tab "Options"
  • Make sure "Enable session state" is enabled, and increase the value. Personally I prefer 60 minutes.
• Enable content expiration for the webserver (so nobody screws up their data using the back/foreward buttons in their browser)
  
  • Open the properties for your DNN site in your IIS manager
  • Go to the tab "HTTP Headers"
  • Make sure "Enable content expiration" is enabled and set your desired expire-time. Personally I prefer immediate expiration.
• Increase the session time-out for your DNN portal
  • Log in as Host
  • Go to the Host/provider configuratino page
  • Open the "Advanced" section
  • Increase the number of minutes users can be online without interaction
  • Save the setting
• Adjust the forms timeout for .NET web applications on your site
  • Open your web.config file
  • find the forms tag
  • Set the timeout value to whatever you like. The new default value for DNN is 60, but in older files (or sites where someone messed with the value) it might be lower. I prefer timeout="60" which also matches the above.
• Cycle/restart your IIS server

Someone have other suggestion.