so i tried to do some internet financial stuff recently, and FF and IE on my home lappy, FF and Kon on the home desktop, and my G1 all returned invalid certificates by unknown issuer to log in. so i didn't use the web and phoned in to deal with being on hold. extra fees were waived for speaking to a rep since i couldn't log in, but as a 4x check my parents machine running *older* FF and older kubuntu recog.. hello... FF spell checker on kubuntu doesn't recognize the word kubuntu or ubuntu... recognized the cert as being a valid verisign certificate valid through next year. any ideas on what's going on there?
Somehow your machine is holding on to expired certificates. First identify the certificate(s) that has(have) trouble. Then go to Internet Options -> Content -> Certificates. Inspect all tabs for those certificates and remove them. Delete temporary cache, cookies and history in IE. Reboot computer (this will remove anything cached in memory). Try to visit the site(s) again and you should be prompted to accept their new and valid certificates. Do the similar operations in FF.