[PHP-DB] sessions and page has expired warning

[olinux]

I am using sessions to store variables until all forms have been filled out. at this 
point they are put into the db.
I would like to know how i can eliminate the problem that occurs when the user presses 
the back button.  I receive a "warning, page has expired... press refresh" I know that 
pressing refresh works fine, but some people do not understand and get confused. How 
can i fix this? 

thanks much 
olinux