This is an error I made and I thought sharing this will prevent other from searching in the wrong direction (as I did).
When installing the SOA Suite you might want to integrate this with the OID. However there is a small problem when during the setup of the SOA Suite two OC4J's are created.
You will have oc4j_home and oc4j_soa for example.
When you integrate the OID into the SOA Suite you will need to manipulate the jazn.jar file in the oc4j configuration directory.
As you have two oc4j's you need to copy the jazn.xml to the respective directories - otherwise you will get to the SSO page but will never be able to log in.