lol odd; myself i dont use it on my forums, i use it everywhere else; You may want to take and check to make sure blacklist.dat (or whatever you named it) exists and can be written to, i have mine 777.
the only differance to what i'm using and what you'd be using is that you're using the full path to the file as i use the relative path ot it; but it shouldn't effect it at all differantly...
I'll take a gander at it later when i'm at my pc; just had the telephone repair guy out and i can't get to my computer