This error is caused by a certificate issue of some kind that prompted the Certificate Authority (CA) to distrust the certificate.  You can attempt to gather more information on your certificate by entering your secure domain here in the checker tool: 
  • Go here: DigiCert SSL Checker 
  • Enter your secure domain - https://mywebsite.org
  • Revocation reason will be listed along with various other facts about the certificate.
Revocation reasons: 
  • unspecified (0)
  • keyCompromise (1)
  • CACompromise (2)
  • affiliationChanged (3)
  • superseded (4)
  • cessationOfOperation (5)
  • certificateHold (6)
  • removeFromCRL (8)
  • privilegeWithdrawn (9)
  • AACompromise (10)
If a certificate shows as revoked in one browser and not another then it is typically caused by a delay in how often that browser checks the CRL (Certificate Revocation List).  You should contact your Certificate Authority (Digicert, Symantec, Geotrust) to determine if any action or review can occur, or if a new certificate will need to be issued.