Help: Session handling in PHP

HI,
I am currently working on my final year project on social networks. I am using PHP and mysql for the same.

But I have encountered a problem with the session handling being used in the project. Whenever I choose to go back to the previous page by clicking on back button it gives the error "Confirm Form Resubmission .This webpage requires data that you entered earlier in order to be properly displayed. You can send this data again, but by doing so you will repeat any action this page previously performed. Press Reload to resend that data and display this page." in the browser.

Any suggestions for the above given error shall be helpful. Thanks in advance.