Unable to upload a .pem file: Unable to set the private key: Probably, the private key format is invalid.

Symptoms

Unable to upload an SSL certificate issued by CA, it fails with the following error message:

Error: Unable to set the private key: Probably, the private key format is invalid.

Cause

None of the certificate files provided by CA (.PEM and .CRT files) contain the private key

Resolution

1. Contact CA to request a certificate including the private key section, it should look as follows:

   -----BEGIN PRIVATE KEY-----
   ...
   -----END PRIVATE KEY-----

2. Add the complete certificate parts to Plesk