I ran into this problem. There are two things you can do:
Reinstall Liveupdate from the Symantec website, which MIGHT work.
OR
Do what I should have done and get rid of Norton and install AVG Antivirus (it doesn't cost a thing to download or update and it works better):
free.grisoft.com
That error is very common with Norton. When it does that, you might as well forget about it.