If your certificate worked prior to March 2015, and you're now seeing the following error, you might need to re-key your certificate:
This happened because Google stopped supporting certificates using the SHA-1 hash (an encryption algorithm) in March 2015 and now requires SHA-2. As a best practice, all certificates should use SHA-2 anyway (more info).
Your certificate's encryption algorithm displays in the Encryption Strength field.
If your Encryption Strength is only SHA-1, you need to update your certificate to use SHA-2 (more info).