When trying to update the Plesk license key via web interface the following error is shown:
*Unable to connect to license server https://ka.plesk.com:5224/xmlrpc.
cURL error description: Problem with the SSL CA cert (path? access rights?)(77)*
nss-softokn-freebl updates for CentOS 6/CentOS 7/RedHat EL6 installed on Plesk server.
Connect to the server via SSH and restart sw-engine:
# service sw-engine restart