This is a common problem. You will need to disable cache from the browser. I suppose you are not able to do any action after you press the back button as the session is invalidated and I hope that in your code you've appropriate checks to validate the user's session. So assuming that, you just need to stop the browser from storing your page in cached. Searching in the forum or google would give you good results. This is one of my search in the forum...
Thanks Ankit for your reply.
You are right .After back ,i am not able to do any thing.I am getting null pointer exception.
But how to disable cache from broser ?
Is there any specific code for that?
If you have any idea please guide me.thanks once again.