replace some work into other string (Messagebox)

I am new in clarion and I have a procedure ds_Message for using
Capesoft MessageBox
I need to modify this, searching into messagebox some word and
replacing it for other but it is not working, I been trying on
differents ways but I can not see the error.
this is my code
Plis could anybody help me!!!!

Data
Locate long
Code

   Loc:sOldMsgText = clip(LMBD:MessageText)

   strreplace = 'mynewword'
   strfind = 'myoldword'

   IF UPPER(strfind)<>UPPER(strreplace)
      LOOP
        Locate = INSTRING(UPPER(strfind), UPPER(Loc:sOldMsgText), 1,
Locate)
        IF ~Locate THEN break.
        Loc:sOldMsgText = SUB(Loc:sOldMsgText,1,Locate-1) & strreplace
& SUB(Loc:sOldMsgText,Locate+LEN(strfind), LEN(Loc:sOldMsgText))
      END
   END
    LMBD:MessageText = Clip(Loc:sOldMsgText)

thanks,