I am having the same issue and I just stumbled into it yesterday. I tried to double-click live update and/or the NIS control panel, neither would open and the error returned was 8504,100. I also, used the removal tool and reinstalled NIS 2011 several times without success. What was interesting is everything looked good, then I would see popup from the tray icon area saying the NIS firewall was disable, then one would say the antivirus was disabled, etc. Even though it looks to be okay (green check in icon) it is not. Any help would be appreciated. I seem to have more issues with this NIS product than any I have ever used. I use AVG without issue at the office. The reason I like the NIS product is the online safety minder application for my kids.
[edit: Clarified subject.]