Oracle Forms

Hi!
I've a block with four items and i only want to show one of them.
So i 've set the property visible to false.
But then when i set the property back to visible is true
i can't insert a new value.
Here is my code:
Declare
it_id_CHA Item;
it_id_INT Item;
it_id_REA Item;
it_id_DAT Item;
Begin
it_id_CHA := Find_Item('BM_ATTRIB.ATTRIB_CHA');
it_id_INT := Find_Item('BM_ATTRIB.ATTRIB_INT');
it_id_REA := Find_Item('BM_ATTRIB.ATTRIB_REA');
it_id_DAT := Find_Item('BM_ATTRIB.ATTRIB_DAT');
if (:STD_BM_ATTRIB.ATTRIB_TYP = 'CHA') then
SET_ITEM_PROPERTY(it_id_CHA,VISIBLE,PROPERTY_TRUE);
SET_ITEM_PROPERTY(it_id_CHA,ENABLED,PROPERTY_TRUE);
SET_ITEM_PROPERTY(it_id_CHA,INSERT_ALLOWED,PROPERTY_TRUE);
SET_ITEM_PROPERTY(it_id_INT,VISIBLE,PROPERTY_FALSE);
SET_ITEM_PROPERTY(it_id_REA,VISIBLE,PROPERTY_FALSE);
SET_ITEM_PROPERTY(it_id_DAT,VISIBLE,PROPERTY_FALSE);
elsif (:STD_BM_ATTRIB.ATTRIB_TYP = 'INT') then
SET_ITEM_PROPERTY(it_id_INT,VISIBLE,PROPERTY_TRUE);
SET_ITEM_PROPERTY(it_id_INT,ENABLED,PROPERTY_TRUE);
SET_ITEM_PROPERTY(it_id_INT,INSERT_ALLOWED,PROPERTY_TRUE);
SET_ITEM_PROPERTY(it_id_CHA,VISIBLE,PROPERTY_FALSE);
SET_ITEM_PROPERTY(it_id_REA,VISIBLE,PROPERTY_FALSE);
SET_ITEM_PROPERTY(it_id_DAT,VISIBLE,PROPERTY_FALSE);
elsif (:STD_BM_ATTRIB.ATTRIB_TYP = 'REA') then
SET_ITEM_PROPERTY(it_id_REA,VISIBLE,PROPERTY_TRUE);
SET_ITEM_PROPERTY(it_id_REA,ENABLED,PROPERTY_TRUE);
SET_ITEM_PROPERTY(it_id_REA,INSERT_ALLOWED,PROPERTY_TRUE);
SET_ITEM_PROPERTY(it_id_INT,VISIBLE,PROPERTY_FALSE);
SET_ITEM_PROPERTY(it_id_REA,VISIBLE,PROPERTY_FALSE);
SET_ITEM_PROPERTY(it_id_DAT,VISIBLE,PROPERTY_FALSE);
elsif (:STD_BM_ATTRIB.ATTRIB_TYP = 'DAT') then
SET_ITEM_PROPERTY(it_id_DAT,VISIBLE,PROPERTY_TRUE);
SET_ITEM_PROPERTY(it_id_DAT,ENABLED,PROPERTY_TRUE);
SET_ITEM_PROPERTY(it_id_DAT,INSERT_ALLOWED,PROPERTY_TRUE);
SET_ITEM_PROPERTY(it_id_INT,VISIBLE,PROPERTY_FALSE);
SET_ITEM_PROPERTY(it_id_REA,VISIBLE,PROPERTY_FALSE);
SET_ITEM_PROPERTY(it_id_CHA,VISIBLE,PROPERTY_FALSE);
end if;
GO_BLOCK('BM_ATTRIB');
do_key('execute_query');
End;

Which properties must i set?
Thanks for help.
With best regards
Nicole