Yes, since you are continuing the troubleshooting I'd go ahead and uninstall Norton, and anything else you think might be holding you back, you can always reinstall later!
.NET updates failing are in a class of their own!! You'll need to uninstall ALL .NET updates, and then install them in a certain order.
Use this first, .NET Framework cleanup tool
http://go.microsoft.com/fwlink/?LinkID=121918Here is the correct order, and direct links for each installer are posted at the page below:
1. .NET Framework 3.5 SP1 (this will install the 2.0 SP2 and 3.0 SP2 )
2. .NET Framework 1.1
3. .NET Framework 1.0
4. .NET Framework 4
http://blogs.msdn.com/b/astebner/archive/2010/12/22/10108400.aspxBack to Norton. Yes, you'd think disabling or temporary disable would actually disable antivirus apps, but I often find it does not but only appears to do so. You can test and see if it's being disabled for real or not, try saving this text in a notepad with Norton disabled, if it allows you then it's disabled, if not then you'll know it's running!
X5O!P%@AP[4\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*
Even if it is actually being disabled, it might be best to go ahead and uninstall it just to rule it out, you can re-install it later!
Hope you can get this sorted without a clean install! I know it's often the quickest and easiest route, but I know how you feel wanting to keep the current system up and running, so good luck!