The most likely cause for the one-X Portal for IP Office service not working and remaining yellow in the platform view of the services is a password mismatch. The mismatch is between the EnhTcpaService service user in the IP Office system's security settings and two of the providers within the portal configuration (the Default-CSTA-Provider and the Default-DSML-IPOProvider).
This password mismatch causes the IP Office to automatically lock the EnhTcpaService user account.