There is an option in php named "Register Globals." In times past, all php servers ran with this option enabled. But it has been found that it can be a severe security problem and more and more servers are doing away with it. In fact, in the latest version of php, it has been completely removed.

Oscommerce, prior to version RC2, was setup to work with this option enabled. If your shop is on a server that has it disabled, or you just prefer the added security (recommended) having it turned off offers, then this change should be installed.