Since July 2010 the Certification Authorities switched to 2048bit RSA Keys, so new root certificates must be installed for all new certificates to work correctly.
If new root certificates are not installed – this can cause problems with the correct installation of the certificate and its recognition by some of the browsers.
Links to CA pages where you can download new root certificates are given below.
RapidSSL Certificate
GeoTrust SSL Certificates
Thawte SSL Certificates
