inconsistent Data Type -ORA-00932
The type InstalmentList is a nested table of InstalmentEntry, so you need to build a set of InstalmentEntry objects to get the list.

The following query works on 11.2:

SELECT column_value AS list, rownum AS rownumber
  FROM TABLE(powermultiset(
               CAST(MULTISET (SELECT InstalmentEntry(1, 1) /*Entry "constructor"*/
                                FROM dual) 
                    AS InstalmentList)
             ));