From: http://www.uluga.ubuntuforums.org/showthread.php?t=1360080

I tried

killall notification-daemon
ps auwxf|grep notification-daemon|grep -v grep # to see if it was still running
#[
killall -9 notification-daemon
#or
kill -9 $(ps ux|grep notification-daemon |grep -v grep|awk ‘{print $2}’)

for those really stubborn processes (try without -9 first!)

#]
#and when that seemed to work I did
sudo apt-get -y remove notification-daemon
#and I also did
sudo apt-get -y remove notify-osd pidgin-libnotify # but I don’t think that last one is needed