TextArea.setFont is it ok ?

I want use textArea on a watchface. and i want to use change font to use my font. but i have an error at compilation :

Error: Unhandled Exception
Exception: UnexpectedTypeException: Unexpected font type, expected Number or Array
Stack: 
  - setFont() at T:\mbsimulator\submodules\technology\monkeybrains\virtual-machine\api\WatchUi.mb:4633 0x300048c4 
  - onUpdate() at D:\workspace\eclipse\Facestive\source\FacestiveView.mc:246 0x10001334 

246 : AgendaTextArea.setFont(FONT_libPerso);
247 : AgendaTextArea.draw(dc);

in onLayout i declare :

FONT_libPerso = WatchUi.loadResource(Rez.Fonts.FONT_personnelle);

in onShow i declare :evtAgendaTextArea = new WatchUi.TextArea({
            :text=>"",
            :color=>Graphics.COLOR_BLACK,
            :font=>Graphics.FONT_SYSTEM_XTINY,
            :locX =>36,
            :locY=>132,
            :width=>170,
            :height=>78
        }); 

when i mask line 246, application is ok.

Can you help me : can you say to me what is the problem ?

Thanks