A few days ago we updated our SSL certificates. The algorithm used to sign these certificates (SHA256) presented problems with some older clients and operating systems, notably WebOS and Nokia devices. To fix this we got our CA (DigiCert) to re-sign the certificates using the older SHA1 algorithm, which should work pretty much everywhere. These certificates are now live on all of our domains.
Most users should not notice any change. If you are on a device or client where you've had to install the DigiCert root certificate in the last few days, you may need to do this again as these certificates are signed from a different root certificate. If that affects you, the root certificate is available from DigiCert's root certificate page and is called "DigiCert High Assurance EV Root CA". If you also need the intermediate cert, its available from the same page with the name "DigiCert High Assurance CA-3".