Ubuntu 16.04 error with apt-get update

Question

I installed the Ubuntu 16.04 LTS and when I insert # apt-get update on Terminal, it returns these errors

E: Failed to fetch http://br.archive.ubuntu.com/ubuntu/dists/xenial-updates/main/dep11/Components-amd64.yml.gz  
E: Failed to fetch http://br.archive.ubuntu.com/ubuntu/dists/xenial-updates/universe/dep11/Components-amd64.yml.xz  Hash Sum mismatch
E: Failed to fetch http://br.archive.ubuntu.com/ubuntu/dists/xenial-updates/universe/dep11/icons-64x64.tar.gz  
E: Failed to fetch http://br.archive.ubuntu.com/ubuntu/dists/xenial-updates/multiverse/dep11/Components-amd64.yml.xz  
E: Failed to fetch http://br.archive.ubuntu.com/ubuntu/dists/xenial-backports/main/dep11/Components-amd64.yml.xz  Hash Sum mismatch
E: Failed to fetch http://br.archive.ubuntu.com/ubuntu/dists/xenial-backports/universe/dep11/Components-amd64.yml.xz  
E: Failed to fetch http://br.archive.ubuntu.com/ubuntu/dists/xenial-backports/multiverse/dep11/Components-amd64.yml.xz  
E: Some index files failed to download. They have been ignored, or old ones used instead.

The sources.list is below

#deb cdrom:[Ubuntu 16.04.1 LTS _Xenial Xerus_ - Release amd64 (20160719)]/ xenial main restricted

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://br.archive.ubuntu.com/ubuntu/ xenial main restricted
deb-src http://br.archive.ubuntu.com/ubuntu/ xenial main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://br.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
deb-src http://br.archive.ubuntu.com/ubuntu/ xenial-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## universe WILL NOT receive any review or updates from the Ubuntu security
## team.
deb http://br.archive.ubuntu.com/ubuntu/ xenial universe
deb-src http://br.archive.ubuntu.com/ubuntu/ xenial universe
deb http://br.archive.ubuntu.com/ubuntu/ xenial-updates universe
deb-src http://br.archive.ubuntu.com/ubuntu/ xenial-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://br.archive.ubuntu.com/ubuntu/ xenial multiverse
deb-src http://br.archive.ubuntu.com/ubuntu/ xenial multiverse
deb http://br.archive.ubuntu.com/ubuntu/ xenial-updates multiverse
deb-src http://br.archive.ubuntu.com/ubuntu/ xenial-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://br.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse
deb-src http://br.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
deb http://archive.canonical.com/ubuntu xenial partner
deb-src http://archive.canonical.com/ubuntu xenial partner

deb http://security.ubuntu.com/ubuntu xenial-security main restricted
deb-src http://security.ubuntu.com/ubuntu xenial-security main restricted
deb http://security.ubuntu.com/ubuntu xenial-security universe
deb-src http://security.ubuntu.com/ubuntu xenial-security universe
deb http://security.ubuntu.com/ubuntu xenial-security multiverse
deb-src http://security.ubuntu.com/ubuntu xenial-security multiverse

deb http://members.change-vision.com/repos/apt/ astah main

The OS is new on my computer, I just install some softwares. I took all the # of the deb and deb-src from sources.list and insert the last line on the file.

I have no idea what can occoured these errors.

Answer 1

I've had the very same problem. After much of research the solution worked for me was to remove all authentications keys (Software Sources -> Authentication, remove all one by one).
After that reinstalling missing keys with y-ppa-manager. Detailed instruction how to do it from here:

1. To install it, first add the webupd8 repository for this program:
   sudo add-apt-repository ppa:webupd8team/y-ppa-manager

2. Update your software list and install Y-PPA-Manager:
   sudo apt-get update
sudo apt-get install y-ppa-manager

3. Run y-ppa-manager (i.e. type y-ppa-manager then press enter key).

4. When the main y-ppa-manager window appears, click on "Advanced."

5. From the list of advanced tasks, select "Try to import all missing GPG keys" and click OK.

After that just close the y-ppa-manager and do update/upgrade, all should be without errors now.