Just to bump this as I'm also getting this error since I plugged the wan into a new router with dhcp on the router.
AMD64 2.1 release with openvpn.
Nov 14 04:00:22 check_reload_status: Reloading filter
Nov 14 04:00:22 check_reload_status: Restarting OpenVPN tunnels/interfaces
Nov 14 04:00:22 check_reload_status: Restarting ipsec tunnels
Nov 14 04:00:22 check_reload_status: updating dyndns WAN_DHCP
Nov 14 04:00:03 php: rc.interfaces_wan_configure: The command '/sbin/dhclient -c /var/etc/dhclient_wan.conf msk0 > /tmp/msk0_output 2> /tmp/msk0_error_output' returned exit code '1', the output was ''
Nov 14 04:00:03 php: rc.interfaces_wan_configure: The command '/sbin/ifconfig 'msk0' inet delete' returned exit code '1', the output was 'ifconfig: ioctl (SIOCDIFADDR): Can't assign requested address'
Nov 14 04:00:00 check_reload_status: Configuring interface wan
Nov 14 00:05:59 kernel: re0: promiscuous mode enabled
Edit:
Should add that going into the wan interface and clicking save then apply brings the nic back up again, so a sort of work around but not ideal for the hours its down until its checked and the above action carried out.
Gonna try it without openvpn servers installed and see if that makes a difference for now as openvpn isnt essential for the next few weeks.
Edit2
Dont know if this is relevent
https://groups.google.com/forum/#!msg/tunnelblick-discuss/NVJunGLxngE/EkjCRMgHfzYJ
"2013-06-20 08:16:17 /sbin/ifconfig tun2 delete
ifconfig: ioctl (SIOCDIFADDR): Can't assign requested address
2013-06-20 08:16:17 NOTE: Tried to delete pre-existing tun/tap instance – No Problem if failure"