[gtkada] runtime error

[yoann toussaint]

hello,
I would like to get a gdk_image from a gtk_drawing_area,
so I use the get function :

 procedure Gdk_New
     (Image      :    out Gdk_Image;
      Image_Type : in     Gdk_Image_Type;
      Visual     : in     Gdk.Visual.Gdk_Visual;
      Width      : in     Gint;
      Height     : in     Gint);

like that :
win:gdk_window;
drawing:gtk_drawing_area;
width,height:gint;
      Win:=Get_window (drawing);
      Get_Size (Win, Width, Heigh);
      Gdk.Image.Get(image,Win,0,0,Width,height);

the compilation is successful, but the previous code line provoke a 
abnormally exit:
Gdk-ERROR **: BadMatch (invalid parameter attributes)
  serial 274 error_code 8 request_code 73 minor_code 0

is anyone knows why and what does error_code 8 it means ?

thanks for help,
yoann