Resolution:
When creating a domain with application data stored on a DB2 database in TRA5.6, a buffer pool with 32k pagesize is required.

Following exception might be encountered in case you use pagesize less then 32k:

[Mon Feb 02 15:48:35 EET 2009] -- Error -- java.lang.NullPointerException
    at com.tibco.pof.authorization.AuthorizationDomain.install_5_1_3(AuthorizationDomain.java:225)
    at com.tibco.pof.authorization.AuthorizationDomain.install(AuthorizationDomain.java:159)
    at com.tibco.administrator.domain.DomainConfiguration.createDomain(DomainConfiguration.java:1602)
    at com.tibco.administrator.du.task.createdomain.CreateDomainTask.a(CreateDomainTask.java:612)
    at com.tibco.administrator.du.task.createdomain.CreateDomainTask.execute(CreateDomainTask.java:454)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:79)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:618)
    at com.tibco.administrator.wizard.progress.Trampoline.invoke(Trampoline.java:96)
    at com.tibco.administrator.wizard.progress.BusyWait.run(BusyWait.java:267)
    at java.lang.Thread.run(Thread.java:810)