Debug shopping cart scripts

I have a couple of sites that are based on the open source shopping cart: [login to view URL] The web host has recently made some changes, they upgraded to have 5.16.3 Perl on the server (before the upgrade it was 5.10.1). This has caused the cgi scripts to become inoperable. They function, but do not pass any form data or link data which results in only loading the home page. Clicking any links or submitting any information to the script simply loops back to the home page. The script ran fine prior to the web host upgrade. I am looking for someone to debug this perl/cgi script and provide me with instructions for repairing the script.