Então aqui está a resposta finalmente:
O Entourage 2004 não consegue encontrar os certificados no Mac OS X 10.5 porque eles se tornaram obsoletos.
As it turns out, the X509Anchors file, as of Leopard, has been made obsolete - but not entirely... It can (and is) still read from, but cannot be written to - at least not with any GUI interface like Apple Keychain or Microsoft Cert Manager.
As Entourage looks at this X509Anchors file for the Root Certificate and not in the new SystemCA/RootCertificates.keychain files, of course it's not going to find it! This also explains why people that upgraded rather than fresh
Fonte: link