SamC,
If the other suggestions do not work, then you may want to try reinstalling NIS 2010 again, since you installed NIS 2010 while bits of McAfee were possibly still around. If NIS 2010 is the only Norton product on your computer, then you can use the Norton Removal Tool method.
Note: the removal tool will wipe out your settings and any other Norton products installed on your computer. It will not touch your product key, however, and your newly installed Norton product should pick up your key automatically.
-Also, if you use Identity Safe, back up your Identity Safe data beforehand:
http://service1.symantec.com/SUPPORT/nco.nsf/0/e5a44e06f97b3f89882572260060120f?OpenDocument&seg=hm&lg=en&ct=us
-download the removal tool from here and save it to your desktop:
http://www.symantec.com/norton/support/kb/web_view.jsp?wv_type=public_web&ssfromlink=true&sprt_cid=1a13409b-29db-4397-a286-9dec49f8e252&seg=hho&ct=us&lg=en&docurl=20080828154508EN
-download the full NIS 2010 installation package from here and save it to your desktop:
http://www.norton.com/nis10
-make sure you have got your product key handy (you can get it from your Norton account) just to be on the safe side.
-deactivate any other security software you may have, such as Windows Defender. However, please leave Norton running. As a side note: running two real-time security programs on one machine is not recommended.
-if you wish, you can create a system restore point
-disconnect physically from the internet (remove the internet cable) that way your computer is not exposed.
-if you're in Vista: right-click on the removal tool icon, run as administrator; run the removal tool 2-3 times, rebooting each time after every run
-after running the removal tool: if in Vista: right-click NIS 2010 icon, run as administrator, let it install itself. When it wants to connect with the web, connect again to the internet.
Please post back with the results if you decide to go this route.