There may not be a corresponding 'private key' or 'pending request' or the key that is found is not the one that matches the certificates.

In order to correct this we recommend you create a new CSR and send that to support to have the certificate re-issued.

Click to find the details on creating a CSR

If you are using an apache based system, then search your server for files ending .key as the file might be in a different location than the one you are referencing in the httpd.conf file