On Mac OS X 10.5, the launchd you talk to as non-root user is not the same launchd you talk to when root. So
$ launchctl list
$ sudo launchctl list
print out different lists, and the unprivileged `launchctl list` contains processes that the root-`launchctl list` does not know about. So running a launctl command as root may cause it to fail.
I have never seen another UNIX-ish tool that would fail when run as root, but succeed otherwise.