Well, since I have in the last few weeks gotten two comments on an old post - August 28, 2002 :

Yesterday was fun - has anyone else seen Norton Anti-Virus corrupt itself to the point where a full uninstall/reinstall fails? The online tech support points to a registry problem, but it all looks fine. I'm building a spare system to replace the flaky one with.

"Error: 1606 Could not access network location \Symantec\Norton AntiVirus Corporate Edition\7.5"

We ended up uninstalling MSIE, then reinstalling it and applying all patches and SPs as needed. Then NAV worked fine!

It appears (from other sources) that NAV requires the Microsoft Update program to be working perfectly to allow NAV to install. I don't understand it, but there it is. The MU program is installed with MSIE 6 and better, so if you don't have 6, upgrade, and if you do, reinstall.