Security Certificate Errors

When I go to some websites such as "staples.com" using XP Home Edition and
IE7, I get a message bar at the top of the page which says "...Internet
Explorer has blocked this website from displaying content with security
certificate errors...".

Here's what I have done to correct the problem so far:
Install the patch described in Security Bulletin MS01-017
In IE7 I went to: "Internet Options | Content | Certificates" and
removed all the expired certificates including the ones on the "Untrusted
Publishers" tab.

The above actions were recommended on some of the chat forums, but they did
not solve the problem.

I have 2 other computers with XP and IE7 installed, and they do not have
this problem even though they have "Check for publisher's certificate
revocation" selected in "Internet Options | Advanced | Security".

Where do I go from here? Any suggestions?