problem with check_dhcp in nagios

[Reinhard Haller]

Hi,

I'm trying to test the dhcp server with

./check_dhcp -i em1 -v

and got

DHCP socket: 3
Error: Couldn't get hardware address from em1. sysctl 2 error - No such
file or directory.

nagios 3.1.2
nagios-plugins 1,4,13,1
FreeBSD 7.2 (amd64)

Any suggestions?

Thanks
Reinhard Haller