[Zope] Changing file ownership

Using an external python method I am trying to change the group ownership of a directory on a Red Hat 6 server. Here is the line of code in question: os.system('chgrp -R extranet /web/htdocs/clients/test') When run from the command line it works fine or if run as a python program from the command line it works fine, but if run as an external method it doesn't work. An "Operation not permitted" error occurs if I try to do the same thing using the os.chown(path, UID, GID) command in the external method. I'm assuming it has something to do with the permissions that Zope/Python is running under. (user:nobody) Any suggestions or insights about how to accomplish this task from an external method? Thanks, Eric