Bearing your signature in mind, another way to update your machine could be copying and pasting this command in a terminal:
Code:
sudo apt-get update; sudo apt-get upgrade -y
You'll have to supply your user password when asked. Before the semi-colon refreshes the repository data, after the semicolon actually upgrades your system now that it knows what the latest package versions available are.
I don't know how to solve that problem exactly, but I do know this is definitely a workaround.