If you are using Windows Vista running Internet Explorer 7 with Norton 360, when you try to access any secure website you might get a warning telling you that "This organization's certificate has been revoked." That includes this site as well, when you click any of the "Add to Cart" buttons.
This is not because of any problem with the certificate (in our case, it would be PayPal's certificate, since clicking an Add to Cart button takes you to a PayPal shopping cart), but rather it is due to a conflict between Norton 360's Transaction Security settings and Internet Explorer 7 running in Microsoft Vista.
Symantec (Norton) is aware of this issue and has issued a fix in an update to Norton 360. If you experience this problem, you may run Live Update to update your Norton 360. Click here to go to Symantec's page describing the problem and the solution.
You can test for this problem by clicking the Paypal advertisement at the bottom of this page. If you receive a warning that PayPal's certificate has been revoked, run the Live Update on your Norton 360.