the port should allways be just a number, adding /sabnzbd makes no sence.
can you ping "NAS"?
if not does your DNS works correctly? (you can try altering your hostfile instaid)
can you access http://NAS:8800/sabnzbd
if you can't connect maybe there is a firewall active?
there could be some caching problem with Internet Explorer. i sometimes can't connect to my host via a hostname. when i choose anther alias of my host it does work. I have this problems with other gadgets two. (tip: you can allso use the computername of the host)
still i think using the IP instaid of NAS should work two. do you still have the problem with the dot's missing in the ip address? (in that case it looks like you are running an older version). try switching from NAS to the ip and back.
if that all doesn't solve your problem you can add me on msn: firstname.lastname@example.org
did you set your host in the sabnzbd configuration?
host = 192.168.254.252
port = 8800