Norton 2011 For Mac fails to download update data and download update data so slow

I have 2011 norton security for mac, and yet live update often failed, and everytime re update live update after a fail, it takes forever to download 110MB or around that of update data even though I have 23Megabit/second download speed.  It seems 2011 Norton Security for Mac is download update data at 110Kilobyte/second or something like that!  How can I fixed this?  Thanks...  How about stop live update from failing also?