I have ZA security suite (11.0.768.000) --and I had the same problem -- I used all the methods shown above -- then was unable to re-install ZA under normal windows -- I was ABLE to re-install while in Win 7 (64) safe mode -- then tried to update -- failed with errors both in safe and in normal windows.

contacted ZA support - was told to go to control panel - internet options - connections - LAN settings. found that the box for "Use a proxy" was checked.....unchecked it -- said OK twice.

SUCCESS -- both the anti-virus/anti-spyware definitions and the product update were able to update WITHOUT errors.........

Thought you guys should know..........