Here's what I did that helped if you are specifically having a problem on Leopard.
My cert was old and needed to be updated. I downloaded this:
http://curl.haxx.se/ca/cacert.pem
Then replaced my cert which was found here on Leopard:
/usr/share/curl/curl-ca-bundle.crt
Reload whatever you have that's accessing it and you should be good to go!