Why are internet certificates untrusted?

This is the error I keep getting when trying to go to sites from safari and firefox. I even got one when I came to the apple support site. My software is up to date what is wrong?

This Connection is Untrusted

You have asked Firefox to connect

securely to www.walgreens.com, but we can't confirm that your connection is secure.

Normally, when you try to connect securely,

sites will present trusted identification to prove that you are

going to the right place. However, this site's identity can't be verified.

What Should I Do?

If you usually connect to

this site without problems, this error could mean that someone is

trying to impersonate the site, and you shouldn't continue.

Technical Details

www.walgreens.com uses an invalid security certificate.

The certificate is not trusted because the issuer certificate has expired.

The certificate will not be valid until 9/8/11 7:34 AM. The current time is 1/1/01 9:49 AM.

(Error code: sec_error_expired_issuer_certificate)

I Understand the Risks