ESXi 4.1, "Unknown Object firewall" !!!

Hello all.

I use Vmware ESXi 4.1 and I want to work with Firewall object but tell me that "Unknown Object firewall", How can I solve it?

[root@ESXHost0 ~]# /usr/sbin/esxcli network firewall

Errors:

Unknown Object firewall

Cheers.