Initial user does not have admin access.
Reproducing the Issue
When login in system with initial user, you do not have access to Administrator work center.
Initial user is not supposed to have admin access since it has to be used only for first configuration.
Once configurations in Business Configuration work center are done, you can go to Business Partner work center and then Service Agents view. There you will be able to create new business users and give them admin access.
KBA , sap_inituser missing access , SRD-FIN-FA , Fixed Assets , How To