AS 10 and hierarchical tree problem

[hudo]

Made a form which uses a hierarchical tree for navigation.
The record group for this tree is initialized in a WHEN-NEW-FORM-INSTANCE.
This works fine on my laptop, where I use database 9, developer 10g.

In production database 8.1.7.2 is used and AS 10.

If I try to deploy my form with the application server (the production
environment) the navigation tree isn't displayed.
What can be the problem ?
It seems to me, that the WHEN-NEW-FORM-INSTANCE trigger is
not evaluated. Here is the code:
-----------------------------------------------------------------
DECLARE
htree ITEM;
v_ignore NUMBER;
rg_navi RECORDGROUP;

tp_id TAB_PAGE;
--
BEGIN
-- Find the tree itself
htree := FIND_ITEM('NAVI_BAUM.HTREE');

--Check for the existence of the record group.
rg_navi := FIND_GROUP('navi');
IF NOT ID_NULL(rg_navi) THEN
DELETE_GROUP(rg_navi);
END IF;

--Create the record Group
rg_navi := CREATE_GROUP_FROM_QUERY('rg_navi',
'SELECT 1 ,level ,mytext ,NULL ,TO_CHAR(nummer) '||
'FROM NAVIGATION '||
'CONNECT BY PRIOR nummer = mylevel '||

'START WITH UPPER(comment) = ''STARTELEMENT'' ');

--Populate the record group with data
v_ignore := POPULATE_GROUP(rg_navi);

--Transfer the data from the record group to hierarchical tree and cause it to dispaly
FTREE.SET_TREE_PROPERTY(htree ,FTREE.RECORD_GROUP ,rg_navi);

END;
-------------------------------------------------------------------

By the way another question: If the AS is used for web-deployment of a form,
is it enough to have a browser installed on a "user pc" ? Or has to be installed some
additional oracle software on the "user pc" ? Which one ?