When you try to update the Plesk license key via web interface you receive the following error:
*Unable to connect to license server https://ka.odin.com:5224/xmlrpc.
cURL error description: Problem with the SSL CA cert (path? access rights?)(77)*
It is caused by update of system packages
nss-softokn-freebl on installed Plesk for CentOS 6/RedHat EL6.
Restart sw-engine with
service sw-engine restart