If you're unable to sign in to the Mac Uploader or stand-alone program, please try setting the 'Keychain Access' preferences for server certificates to 'Best Attempt.' To do this, follow these steps:
- In Utilities, open Keychain Access.
- Choose Keychain Access > Preferences.
- Click Certificates.
- Choose a certificate validation and select Best Attempt in both OCSP and CRL drop-down menus.
- Leave the Priority setting as OCSP. You should now be able to sign in successfully.