error with ndp command for ND proxy

Hello, 

do you have some example for ND proxy configuration?

I want use this on my FW, but when I use ndp command, I have error:
set: cannot configure a new entry

I don't understand.

My archi is:

Internet---router IPV6----FW OpenBSD4.2-------Linux station (startv6)
                  IPv6-1  IPv6-2    IPv6-3    IPv6-4

I try:
ndp -s <IPv6-4> <MAC of IPv6-2> proxy
result: 
set: cannot configure a new entry

I have:
net.inet6.ip6.forwarding=1
net.inet6.ip6.accept_rtadv=0

when I do "ping www.kame.net" on "Linux station"
"icmp6 echo request" go to "router IPV6", 
but there is no reply for
"icmp6: neighbor sol: who has <IPv6-4>"

It's normal, but how can I have reply? ndp is not the good command?

the tcpdump on interface of IPv6-2
---begin---
14:40:02.767141 startv6 > orange.kame.net: icmp6: echo request
14:40:03.116245 fe80::207:cbff:fe0f:3764 > ff02::1:ff23:be89: icmp6: neighbor
sol: who has startv6
---end---

very thank's for your help.

--
Eric JANTZEN - http://cv.jantzen.fr
Lyon
FRANCE