AWS: "Unable to parse certificate. Please ensure the certificate is in PEM format."

The AWS CLI requires file:// prefix for local files. For example file://private.key, file://cert_file, etc.

Just ran into the same exact issue: web console and AWS CLI reporting the same error in not being able to parse the certificate.

The error's root cause turned out to be in the private key -- converting my private key to a "RSA PRIVATE KEY" fixed the issue:

openssl rsa -in server.key -out server.key.rsa

Then, use the server.key.rsa in the private key field and leave the public cert as is.