PHP-SSL problem

Hi, all I have set up ssl site with php, in which there is credit card transaction. My problem is the following. After I fill out the credit card form page in my site and click the button to go the next page, I have error page showing "This page cannot be displayed". This occurs from time to time, it's not always happened, though. The page I am talking about is placed under secure server, which is apache. Without the ssl, the site namely the unsecured site is running very well. The system that the site runs under is freebsd3.0 and has php4.0+mysql+mod_ssl. Since the page is critical I need to find a way to solve this problem. Thank you in advance for any ideas.