The permission problem lead me to the firewall (shorewall).
Try to temporarily disable it with:
shorewall clear
If the problems comes from the firewall, the configuration stored in nethserver database is not correct.
Check with
db networks show,
adjust with
config setprop eth1 ipaddr x.x.x.x netmask x.x.x.x ...
Apply with
signal-event interface-update
This event will restart the firewall.