Comment 20 for bug 56880

I had this problem today with 10.04. The root cause is that environment variables such as http_proxy are not preserved when you use sudo. As a workaround you can get a root shell with:

sudo bash

Then set http_proxy to what it should be:

export http_proxy=http://user:<email address hidden>:8080

Then you can do apt-get install or dpkg --configure -a if you had to manually kill the previous install

HTH