Secure Login/Security Cetificate

[Syzich]

Just a little while ago, I went to a site with a secure login that I frequent. After inputting my user name and password, Internet Explorer brings up its page notifying me that the site I just accessed didn't have it's security certificate issued by a trusted source. Just to be on the safe side, I closed the browser and went back to the site, I double checked the security certificate by clicking on the lock icon next to the address bar and it was indeed issued by a trusted source. I entered my user name and password again and didn't get the notification from IE. I changed my password just to be on the safe side, though. Also, I thought I'd mentioin that I navigated to the site by clicking on the link in my favorites, not from a strange link. So, why did I get the notification from IE about the security certificate? Is it just a bug or error in IE?

IE 7/ XP Home SP2