Which make BADSIG 16126D3A3E5C1192 error occur in my ubuntu 14.04?

Question

I'm newbie using Ubuntu 14.04 and I get BIDSIG 16126D3A3E5C1192 error when I tried to install docker. Error message is

W: GPG error: http://us.archive.ubuntu.com trusty Release: The following signatures were invalid: BADSIG 16126D3A3E5C1192 Ubuntu Extras Archive Automatic Signing Key <ftpmaster@ubuntu.com>

I followed instructions from docker doc and did this

$ sudo apt-key adv --keyserver hkp://­ha.pool.sks-keyserver­s.net:80\
     --recv-keys 58118E89F3A912897C07­0ADBF76221572C52609D
$ echo "deb https://­apt.dockerproject.org­/repo ubuntu-trusty main" | sudo tee /etc/apt/­sources.list.d/­docker.list

If I remember correctly, after I entered it, I installed docker. And then, I installed this

$ sudo apt-get install linux-image-extra-$(­uname -r) linux-image-extra-vi­rtual

but while downloading, I forced close the terminal. After these steps, I start get BADSIG error when I use apt-get update. Is there any steps I've done wrong that lead to BADSIG 16126D3A3E5C1192 error.

For error, I used the following steps and it looks fine now. I tried to solve by removing docker first.And sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 16126D3A3E5C1192 and

$ sudo -i
# apt-get clean
# cd /var/lib/apt
# mv lists lists.old
# mkdir -p lists/partial
# apt-get clean
# apt-get update

but I still get BADSIG error. Then, I tried this and it solve my error but I don't know why.

sudo rm /var/lib/apt/lists/­* -vf
sudo rm /var/lib/apt/lists/­partials/* -vf

and from "Software & Updates", selected server to "Other/Select Best" and sudo apt-get update.