Change Sierra Style Speech Text Background

[Priabudiman]

Hello,

Ive tried the manual and browse the forum to no avail,

In the general, ive changed the speech stle to sierra with background, and i want to change the background with a boxed gui. now ive created a gui, give it a background color and size, bit when i put

Code: ags

game.speech_text_gui=2;

in the global script, when i run the game and test, it says : gui set as text window, but its not actually a text window.

where am i doing wrong, i already change the gui to text window. (right click - New Text Window Gui)

thank you in advance.