Can't use class in an old version...

My client is using the old version of SAP, I think it is ver.4. How will I create a pop-up window that will specify a filepath on the parameter. I can't use

AT SELECTION-SCREEN ON VALUE-REQUEST FOR pfle_hdr.
  CALL METHOD cl_gui_frontend_services=>file_open_dialog
    CHANGING
      file_table = lt_filetab
      rc         = lt_subrc.

it will not be recognize.

Point for the helpful ideas.

Thanks!