IP 127.0.0.1 is restricted for administrative access in Parallels Plesk Panel settings (Restrict Adminisrative Access).
Upgrading Customer & Business Manager failed with error:
Repair local plesk panel:[ FAILED ]
Upgrade has been completed with errors.
Since Parallels Plesk Panel 10.4 Customer & Business Manager and SSO works with Plesk via IP 127.0.0.1 but not via hostname as in previous versions.
Remove 127.0.0.1 from the list of restricted addresses or add to the list of allowed addresses (Tools & Settings > Panel > Restrict Adminisrative Access).