Norton Anti-Virus Auto-Protect could not continue

I have a MacBook and recently upgraded to Mac OS 10.6.6 (Snow Leopard).  Ever since doing so, every time I turn on the computer I get at least 12 consecutive, identical error messages from Norton:

 

"Norton Anti-Virus Error: Norton Anti-Virus Auto-Protect could not continue.  Please run Live Update or reinstall Norton Anti-Virus and restart.  (Code 10)."

 

So I have run Live Update, which seems to be updating three programs. It checks off  two of them,

Live Update for Mac (3.5)

Norton Anti-Virus for Mac (10.1.2)

 

and it tries to update NAV for Mac Virus Defs, but fails.  I've repeated this several times, with the same result: failure.

 

I tried to see if I couldget more current versions of Live Update (mine is dated 2005, I noticed)  and of Norton Anti-Virus for Mac, but couldn't get that information from the website or the Virtual Support mechanism.  I read as many seemingly relevant links as I could. I have given up.  What can I do to upgrade NAV for Mac Virus Defs?

Thanks!