Why I cant update???

I have reinstalled ubuntu. But after reinstalling it, it wont update anymore

Here's the error message

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 intrepid-security 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://ph.archive.ubuntu.com intrepid-updates Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>

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

W: Failed to fetch http://ph.archive.ubuntu.com/ubuntu/dists/intrepid-updates/Release  

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

How can I get rid of this error?

Hello, please post your /etc/apt/sources.list

dannybuntu said: Hello, please post your /etc/apt/sources.list

Where can I see that? I'm totally a linux noob :(

your sources.list is ok, or should be ok, since you did not touch it.

it is found at /etc/apt/sources.list

it's caused by a bad proxy in the repository server, anyhow, try updating in a few hours or so.

-edit

also do..

sudo apt-get clean sudo apt-get update

loell said: your sources.list is ok, or should be ok, since you did not touch it.

it is found at /etc/apt/sources.list

it's caused by a bad proxy in the repository server, anyhow, try updating in a few hours or so.

Ok thanks guys for replying... I think I will change my download server to Main server at this moment..So that I could use this PC later:D