Mcrypt is installed, but error implies it's not.

Thanks Rufnex, but I know that article well. That's a method to get the MAMP interface to display the versions of PHP you already have on your machine. MAMP only shows two at a time. Anyway, what I need, is a configuration or something, that will make MAMP "see" a background process. My background process is bypassing MAMP and thus getting run by the OS-installed version, which is different.