NAV LiveUpdate fails to install downloaded update

I use Norton AntiVirus 2004 on WinXP Home. Just recently I started having a problem with LiveUpdate where it downloads an update called "Norton Antivirus/Product Updates" and appears to install it, except that it stops responding when the installation progress bar reaches the max. There are no error messages ("LUxxxx" or otherwise). I invariably have to use Task Manager to end LiveUpdate, at which point I get a dialog box that says I should run LiveUpdate again to install the update that failed.

This update is very small (approx. 64K) but the installation seems to take a long time before it stops. What's also odd is that other updates will download & install just fine, although I've learned to uncheck the stubborn "NAV" update first. For instance, I installed updates to my virus definitions last night and the process went flawlessly. Any thoughts? Is this a LiveUpdate problem, or NAV? Am I going to have to uninstall NAV and reinstall? I've spent a lot of time in the Symantec Knowledgebase without finding anything. Thanks in advance.