Warning: Page has Expired, HELP

Hello, Hope that someone could help me. Everytime I use the Back button on my browser the page expires. I get this message: Warning: Page has Expired The page you requested was created using information you submitted in a form. This page is no longer available. As a security precaution, Internet Explorer does not automatically resubmit your information for you. To resubmit your information and view this Web page, click the Refresh button. I thought it was my set-up but it does the same thing on the server. My set-up is Apache, PHP and MySQL. Could someone tell me how I can stop this from happening. Thanks David