There are two types of problems I have seen. One is with AMD processors. The other I encountered was MSUpdate downloads did not install. There are a number of articles on the AMD problem - which I did not encounter on one of my AMD machines.
For the download intall problem, I found a program Dial-a-fix, from http://www.softpedia.com
, which solved the problem for this, and for another computer using SP2 upgraded from SP1.
The program is free, donations requested. It does a number of other cleanup tasks.
PS: I had to uninstall Norton 360 before running it, then reinstalled N360. Symantec's downloads for this worked like a charm and were quite quick. BuDump.exe saves information. Norton-Removal-Tool.exe removed all references to Norton/Symantec programs. After running dial-a-fix, I rebooted and found a Norton/Symantec screen directing me to their download screen. It downloaded and reinstalled my Norton 360v2. I had saved my product key, but didn't need it in the reinstall process.