register_globals must be set to On with php.ini for AShop to work.
The register globals feature of php automatically creates variables of all form fields and cookies which is something that is used everywhere in AShop. The reason why it is now turned off by default in php is that it is much safer to handle get fields, post fields and cookies separately to avoid hackers being able to override variable values. To do this would require rewriting a lot of the code in AShop.
It may also be possible to use a code to simulate register_globals on. This could be a quick way to make AShop work regardless of this setting.