Thats where Norton is a pain in the backside, dont get me wrong, regardless of what others say i think it is a good Anti-Virus,however, using it can be as frustrating as having malware on your system, and its a nightmare to get rid of. Ive had first hand experience!
Ive never seen this error,but you could try running and downloading updates from the Symantec site itself instead of letting the programme do it, a slight annoyance,but it may work.
Try reading
THIS and see if it offers any help for you about downloading online.
You can also have a look on the Symantec site
HERE to see these instructions about the problem, although look for other suggestions before you do anything it suggest as there maybe a simple fix that does not require what Symantec instructs.
As i no longer use Norton, i cant really offer any more advice for now on this,but i will continue to look for you.
You could also try turning off you PC for a while and on Restart try again with the updates procedure.
Maybe you could also try 'Google' and 'Yahoo' by typing in your error and seeing what it comes up with. DO NOT feel as if you have to use the first fix you find,look at others too,as some fixes will no doubt tell you to mess with the registry or uninstall and reinstall Norton as the other link suggests ive posted, which may not be necessary and can somtimes cause more harm than good.
Let us know what you find,i hope the Symantec links helps in supplying Infomation on helping resolve your issue.