I seem to get a lot of inquiries about problems installing the SABnzbd+ port or starting SABnzbd+ on these systems. Note that the news/sabnzbdplus port is tested against vanilla FreeBSD systems only, therefore I can't guarantee that it works on FreeNAS or NAS4Free or any other appliance-based system derived from FreeBSD.
I suspect that the problems on these systems arise from the root partition being mounted read-only, as both FreeNAS and NAS4Free are intended to be appliance installations (i.e., not changed) and facilitate solid-state media, like CF cards, for the operating system. It's entirely possible that the root partition is mounted read-only, and as such, the SABnzbd.ini file cannot be created under /usr/local/sabnzbd.
I would suggest attempting to re-mount your root partition read-write (mount -u /), and installing/starting SABnzbd+ from there. Alternatively, you could symlink /usr/local/sabnzbd to a directory on writable media, such as the drives that FreeNAS/NAS4Free are managing in your system.
In the future, please refrain from creating threads about problems with these types of installations unless you've attempted the suggestions above. If there's still a problem and you can give me some sort of details, I can do my best to help you out -- but once again, I make no guarantees on systems that aren't vanilla FreeBSD.