"Failed to load the package list"

When attempting to remove, install or update software through the Ubuntu Software Center, I came upon an error like this...

Failed to load the package list

This is a serious problem. Try again later. If this problem appears again, please report an error to the developers.

E:Could not open file /tmp/aptdaemon-frozen-statussfW5AS/status - open (2: No such file or directory), E:The package lists or status file could not be parsed or opened.

...or like this

What does it mean? What should I do about it?

A lot of times, Software Center freezes or loads slowly or nothing at all, and errors would happen, which seems to be the usual behavior ever since first getting Ubuntu (12.04) and I haven't had time to look at them -- but since these errors came up now as "serious", perhaps someone can help me? :P

Could these problems be caused by an app I've downloaded through the Software Center or Terminal?

Please try this. Just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command below.

sudo rm -r /var/lib/apt/lists/* -vf
sudo mkdir -p /var/lib/apt/lists/partial
sudo apt-get update