I have had similar issues with the "home" versions of NAV (5.0, 2002, etc.) but have had no problems with Symantec NAV Corporate Edition 8.x. I guess that is primarily because a local update server handles the updates for the entire LAN. Personally, I don't use live update for that reason (corruption), but instead I download the updates to the server twice a week from Symantec, and the server takes care of the rest.

NAV isn't the best AV, but it works fine for my purposes. On my gateways, I use McAfee, NAV and Kaspersky layered over each other. McAfee checks the incoming packets, Kaspersky the raw email, and NAV for the local file system. If you tweak them just right, they don't conflict with each other. During my audits, I disable all these AV programs (After the LAN is physically disconnected from the Internet) and manually run AVG on the servers. Never can be too careful.

Yep...I'm paranoid