Looks like this is Windows 2008...? Is it 32 and 64 bit defs that fail to download, or just 32? I don't have a Windows 2008 box at my disposal to verify the paths, and most of our documentation has the XP/2003 file paths.
ETA: I just saw that all of the info from the log you sent has to do with 64 bit defs. Adjust the following accordingly.
1- Try emptying this folder; are you using LiveUpdate Administrator, too?
C:\Program Data\Symantec\LiveUpdate\Downloads
2- Make sure the following folder exists:
C:\Program Data\Symantec\Definitions\SymcData\sesmvirdef32
(there should also be a sesmvirdef64 folder there too)
The LiveUpdate log may also have some information (C:\Program Data\Symantec\LiveUpdate\log.liveupdate).
Thanks,
sandra