executing shell commands

hi everyone,
i am creating a fe for cron.everything works fine except that for the system() command.( the most important part of my code)
<snip>
system("crontab /tmp/crontab.tmp/");
</snip>
any help on why its refusing 2 execute would be greatly appreciated.
Thanks in Advance,
aparna

Have you tried executing the command at the actual command line? Have you checked your error logs? Does the Web user (presumably nobody or www) have access to a crontab? (I doubt it.)