Browser Back not working

[Gavi Raaghav]

We have a web application.When the user traverses from page A to page B and then clicks the browser back button to goto A the page cannot be displayed screen appears,however if then the user clicks the refresh button and submits the page then then page A gets displayed properly.What is the fix for the back button to behave correctly that is without refresing the page shud get displayed.
I am using IE6.0,WAS5.1 and using cookies for Session Management in WAS.