MSN via SAP com TH_POPUP

Este codigo é um mini CHAT usando recurso SAP (ABAP).
REPORT Z_PG_MSN.
TABLES: USR02.
TYPE-POOLS: VRM.
DATA: IT_LIST TYPE VRM_VALUES,
LIST_VALUE TYPE VRM_VALUE.
DATA: MDT TYPE SY-MANDT.
DATA: BEGIN OF USUARIO OCCURS 0,
BNAME LIKE USR02-BNAME,
END OF USUARIO.
DATA: CLIENT LIKE SY-MANDT,
USER LIKE SY-UNAME,
MESSAGE LIKE SM04DIC-POPUPMSG.
 
SELECTION-SCREEN BEGIN OF BLOCK BY1 WITH FRAME TITLE TEXT-200.
PARAMETERS: P_MDT(3) TYPE C,
P_USER TYPE USR02-BNAME AS LISTBOX VISIBLE LENGTH 20,
P_MSN(255) [...]