Using Multiple Casting of collection type - Join them

 I have the following:

create type WMI_ARRAY_NTT AS TABLE OF VARCHAR2(32767)

Cursor is
SELECT a.COLUMN_VALUE itemnumber
            ,b.cu_id
            ,c.COLUMN_VALUE shortdesc
      FROM   TABLE (CAST (v_item_numbers AS wmi_array_ntt)) a
            ,unit_assembly b
            ,TABLE (CAST (v_item_descriptions AS wmi_array_ntt)) c
      WHERE  1 = 1
      AND    b.assembly_item_id = a.COLUMN_VALUE
      AND    a.ROWID = c.ROWID;

I get runtime error saying that rowid is not valid. How do I join these casted collections?

Thanks

Andy