cron won't activate changes

[Ina&Frank <if.frijns@wanadoo.nl>]

Hi all.

I need to block an (internal) ip-address a few hours a day. I added
iptables -I FORWARD -s <ip-address> -j DROP to iptables. Works perfectly.

However when I add this to cron it keeps saying (cron) 'installed 
succesfully'
but is won't do that job.

I added it in /etc/crontab (as root, using crontab -e) and added the line
0 23 * * * root  iptables -I FORWARD -s <ip-address> -j DROP

I use kernel 2.4.18

Fooks, where am I missing the point? Why it won't edit the firewall at 
23:00hrs??

Anyone?

Thanks in advance