Hoping someone can help,

Everytime I try to go to a webpage in Safari that requires a secure connection, I get a message like the above. I tried in firefox, and that will allow me to go to the page, but the little secure padlock is crossed out, so the actual connection is not secure. Would this be a problem with my network settings - I have the osx firewall running, or something wrong on my isp's end (tpg)?

Running 10.3.9 with an adsl connection.

Hope that's enough info - any ideas?

Cheers
James