You probably still have remnants of NIS 2004 on your computer and it is casuing a conflict which is a common problem from what I understand. This link will give you manual removal instructions. Make sure you follow the correct ones for whatever your operating system is.
I had Internet security 2004 and bought the 2005 version. I was instructed to uninstall the 2004 version before installing the 2005. I did all that, but now when I try to install the 2005 Internet Security it bombs out all the time and leaves messages like" This MSI must be launched through setup ".
How do I do that?