Would you mind downloading from the intenret? I mean you will need that anyway to keep your system up to date via apt-get / aptitude.
So check your /etc/apt/sources.list and comment all lines out via # having no http or ftp in front.
On my servers sources.list look like that:
But take this just as an example because I don't know which stuff behind the URLs resides when using any debian based linux like ubuntu.