First, why do you issue the same statement 3 times?

Second, the code does not make sense in the mentioned triggers, as they fire for each record, but the code sets properties for the whole block.

So the question is, what is your desired behavior? Should the user be able to insert new records? should the user be able to update existing records?

How many records do you show in your block? Is the block you want ro disable a different block or it is the same block where your GRN_POSTED is in?

Better try in post_insert trigger.

Dear Mr.NZK,

To restrict modifications based on an item value(pst_yn), you have to write item level trigger for all fields except posted indicator (ex.) pst_yn for example,

when-new-item-instance

     if :pst_yn='Y' then

          if get_item_property('doc_date',update_allowed)='TRUE' then
               set_item_property('doc_date',update_allowed,property_false);
          end if;

     else

          if get_item_property('doc_date',update_allowed)='FALSE' then
                set_item_property('doc_date',update_allowed,property_true);
          end if;

     end if;

To restrict deletions based on an item value(pst_yn), you have to write block level trigger like,

key-delrec

     if :pst_yn='Y' then
          null;
     else
          delete_record;
     end if;

If GRN_POSTED in placed in the Master-Block, i would do the following:

Disable the INSERT_ALLOWED, UPDATE_ALLOWED and DELETE_ALLOWED in the Post-Insert and Post-Update trigger. Additionally, enable ro disable them in the WHEN-NEW-RECORD-INSTANCE-trigger on the master-block.

Your post is not give us much information,

Andreas Weiden raised a big doubt.  The indicator field where is located? Either Header or Detail?...

If it is located at Header then AndreasWeiden solution is suitable for your requirement.