"Security Alert" message box comes up when...

I am trying to log on to "my eBay" page. I've had this happen for a few days now and I can't even logon to the q&a bord to ask what's up!! The "Security Alert" message box says the certificate is one from a site I don't trust even though it's the same link I've used for a year or more. I've tried lowering my explorer sec.level and that doesn't help. I can't exit the page, or delete the message box and the page stays frozen as if it's trying to load. How do I get rid of this!!??

tia.... mitch