I had that same issue, with installing NAV 2002,
Basically, I uninstalled and installed twice and it worked.
After the first install, which I received the script error, when the dialog box pops up and says "configurating NAV...", I cancelled out of it. uninstalled the program. And manually ran regedit and searched and deleted all reg- keys that were left over and all the symantec directories and navnt directory and files...
I installed it again and then it worked....
Not sure if this will work for you... but it did for me.