[Zope] Prb using os.system in product

I'm trying to call a PHP file from python using os.system(), but it always returns -1 (the PHP script is executed, output piped to a new file). The command works from the command line, it also works in the os.system call when running Python interactively. I've also tried something as simple as "touch /path/to/newfile": works in interactive mode, not from Zope. The directory it's writing to has world-writable permissions (777) for testing. I also tried using os.popen to get the output without sending to a file, but the command "f = os.popen( php_cmd)" always returns the EAGAIN os error code. I appreciate any help. Michael