get_*_directory problem

Hello all!

I'm using clase cl_gui_frontend_services, and every time that I try to get a directory using any of its methods I always get an empty string.

I have already tried:

DATA: dir_temp TYPE string.
CALL METHOD cl_gui_frontend_services->get_temp_directory
   CHANGING
     dir_temp = dir temp.

CALL METHOD cl_gui_frontend_services->get_sap_workdir
   CHANGING
     sapworkdir = dir temp.

CALL METHOD cl_gui_frontend_services->get_sapgui_directory
   CHANGING
     sapgui_directory = dir temp.

and all the methods bring an empty string.

Any ideas of what might happen here??

Thanks in advance.

Mauro.