This fix worked for me.
I had the repeated 8504 error and 100 after the NIS program attempted to do a self fix. I downloaded and reinstalled via the NRnR executable. This didn't work, well actually it worked once but failed at the next reboot.
I use Firefox as default and IE is installed on my XP machine which I rarely use. To cut a long story short, I launced IE8 at some point and found this was hanging on the start page and it would not load. Knowing Symantec uses elements of the Microsoft components in NIS, I started to debug the MS disfunction. I tried to fix IE and found none of the MS fixes would work either.
Eventually I downloaded and resinstalled IE8 from the MS support site. Don't try and do a Fix it solution as this depends on some elements (.net) that were either missing or corrupt on my system. Download the entire IE executable and reinstall it. After that NIS worked and has now been stable for two days.
Fingers crossed.
Jim
I have similar issues. Downloaded IE8, will not install, error message says:
"Setup can't continue because a more recent version of Internet Explorer is installed on your computer"
So I tried to uninstall IE, went to Control Panel the Progams and Features, cannot find an IE entry anywhere, not in that window or in the Windows Features window either, any ideas?
I had the same error message when I tried to install IE 7 which I thought I had. I downloaded IE 8 and that did it. As I don't know anything better, you might try downloading IE 9 next or 10 if that fails. Remember to get the complete download version and don't rely on a MS fix it screen.
It's a pity that the Symantec functionality is so tied to IE and it's components.
Jim
This is a follow up and hopefully a clue to what is happening. I returned from vacation today and NIS was still working. Then I applied windows updates and bang, now it's dead again. IE won't launch again. This looks like it's a Micrososft problem.