Accessibility level of a record extension????

Accessibility level of a record extension????

[Pawe� Niewiadomski]

Here is a prototype of my queue package:

-- Program 9.8 Full priority-queue ADT
with ada.finalization; use ada.finalization;
generic
  type item_type is private;
  null_item : item_type;
  with function "<" (x,y: item_type) return boolean is <>;
package g_class_dllist_priority_queue is
  type handle_type is private;
  type queue is limited private;
  function empty(pq: queue) return boolean;
  procedure insert(pq: in out queue; item: in  item_type; 
    handle: out handle_type);
  procedure getmax(pq: in out queue; item: out item_type);
  procedure change(handle: in handle_type; item: in item_type);
  procedure remove(handle: in out handle_type);
  procedure join(pq1,pq2: in out queue);
private
  type node;
  type link is access node;
  type handle_type is new link;
  type node is record
    item: item_type;
    prev, next: link;
  end record;
  type queue is new limited_controlled with record
    head, tail: link;
  end record;
  procedure initialize(pq: in out queue);
end g_class_dllist_priority_queue;

and here is the program I want to test the package with:
with ada.text_io, g_class_dllist_priority_queue, dodatki;
use ada.text_io, dodatki;
procedure testuj is
  	subtype str20 is string (1..20);
    null_str: str20:=(1..20=>' ');
    package queues is new g_class_dllist_priority_queue (str20, null_str, 
"<");
    use queues;
    pq: queue;
    s: str20;
    handle: handle_type;
begin
  ...
  ...
end testuj;

The compiler displays the following error:
testowanie_kolejki_lista.adb: Error: line 6 col 79 LRM:3.9.1(3), The 
accessibility level of a record extension shall not exceed that of its 
parent; this also applies in a generic instantiation
       (In instance of generic g_class_dllist_priority_queue at 
program_09_08.ada: line 25 col 8)

the error is caused by the package instantiation.  I would be grateful if 
someone could explain what it means.  I have tried searching in Reference 
Manual, but as I am not experienced in Ada programming, the explanation 
given by the RM is not clear enough for me.
Thanks in advance
Pawel