If all the conditions below are met, and the problem is not yet resolved, open a problem ticket so that we can investigate the problem:
You have read 5.11 Object-Based Navigation.
You have read all OBN.* related texts in the FAQ.
You have checked table AGR_HIER_BOR to confirm that this OBN target is actually defined in a specific role.
You have used transaction SU01 to confirm that this role is assigned to this user.