The script behind Install Updates menu entry executes the following two commands:
sudo apt-get update && sudo apt-get upgrade
However, the execution of these commands is broken by 404 errors related to invalid repository addresses for Google Chrome and Google Talk:
As shown on the screenshot above, the Terminal window closes
before the second command <sudo apt-get upgrade> is executed and the upgrades are never performed.
The solution is to uncheck both Google entries in the repository settings, which will allow the proper execution of both "update" and "upgrade" commands:
I assume that all this also affects the ability to download Google Chrome and Google Talk Plugin using Install Additional Software menu entry.