To ensure that the manager as the correct access from a People Management perspective:
In Portal, go to the People Management dashboard
Go to Data Centre and select Maintain Org Roles by Person
Check that the manager has the correct Role and Org Group assigned.
However, this issue usually occurs because the manager does not have specific Work Group & Department combination access in CoreTime.
In Back Office, click CoreTime, System Params, System Users
Query the username
Assign correct Work Group & Department combination access to Username
Click Save.