\button does not appear

["Denis B. Roegel" <Denis.Roegel@loria.fr>]

On page 76 of the metafun manual, there is an example
with \button. But when I try to compile the following
file, I can see no button. Actually, no dvi file is generated.
What am I missing?

I am using the TL5 + Sep. 21 context.

Thanks,

Denis

\setupcolors[state=start]
\starttext

\def\MyGraphic%
  {\startreusableMPgraphic{name:\overlaywidth:\overlayheight}
     path p ; p := unitsquare
       xscaled \overlaywidth yscaled \overlayheight ;
     fill p withcolor .625yellow ;
     draw p withcolor .625red ;
   \stopreusableMPgraphic
   \reuseMPgraphic{name:\overlaywidth:\overlayheight}}

\defineoverlay[my graphic][\MyGraphic]
\button[background=my graphic,frame=off]{Go Home}[firstpage]

\stoptext