Why am I getting "Invalid File. File upload canceled." when I try to upload an S/MIME certificate?

Environment:

File Manager, Emails
Oracle B2C Service

Issue:

I am trying to upload an S/MIME certificate in the Additional roots directory from File Manager, but I am prompted to the following message: "Invalid File. File upload canceled."

Resolution:

The file should be in DER Encoded Binary X.509 (.cer or .crt) or Base-64 Encoded X.509 (.pem) format. The Oracle B2C Service application requires that certificates have the correct file extension. Certificates with an incorrect extension will be blocked for upload. Additionally, you may also see this message if the same certificate has already been uploaded (even with a different file name) and it already exists in the hash table.

If you receive this error even though the certificate is in a correct format and it does not already exist, please submit a service request to Technical Support via the Ask a Question page. Technical Support will then work with you to isolate a root cause and determine the best course of action for resolution.*