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

After more testing it looks like MAMP simply doesn't "see" the background process. Since MAMP doesn't see it, the OS-installed version of php (5.5.14) picks up the call and runs with it. That OS-installed version doesn't have mcrypt. There's the rub. The simple solution would be to find out how to get MAMP to recognize background commands. I could simply install mcrypt in the OS-installed version, but then I'd be maintaining two version of PHP. That's not good.