"Page has Expired" Error when hitting on <BACK> button

Hi. I'm using PHP3 to generate some webpages on-the-fly. However, I've a problem whenever I uses the IE browser to browse through the generated webpages, ie, when I clicked on the <BACK> button of the IE browser, I would every time received this error: /==============================/ 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. /==============================/ This problem doesn't seem to occur when I use the Netscape browser. BTW, I didn't use <META> to refresh the content, or use any javascripts to clear the fields of the form. Is there anybody out there know how to solve this problem? Thanks and regards, Raymond Wee