Errors when updating Ubuntu

[DobsonM]

I was using the latest beta of Ubuntu which I installed 3 days ago, with the recent release I am now getting this error in the terminal when running "sudo apt-get update"

W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://nz.archive.ubuntu.com precise Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>

W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://nz.archive.ubuntu.com precise-updates Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>

W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://extras.ubuntu.com precise Release: The following signatures were invalid: BADSIG 16126D3A3E5C1192 Ubuntu Extras Archive Automatic Signing Key <ftpmaster@ubuntu.com>

W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://security.ubuntu.com precise-security Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>

W: Failed to fetch http://nz.archive.ubuntu.com/ubuntu/dists/precise/Release  

W: Failed to fetch http://nz.archive.ubuntu.com/ubuntu/dists/precise-updates/Release  

W: Failed to fetch http://extras.ubuntu.com/ubuntu/dists/precise/Release  

W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/precise-security/Release  

W: Some index files failed to download. They have been ignored, or old ones used instead.

I have purged my PPA's but I get the same errors, what do I need to do? I don't really want to have to do a clean install.

[Rubi1200]

Hi,
try the following commands:

sudo apt-get clean
sudo apt-get install -f
sudo dpkg --configure -a
sudo apt-get update

Run them one at a time and post error messages if relevant.

Also post the output of this:

cat /etc/apt/sources.list