[NTG-context] Problem with usemodule[graph]

Hi, I'd like to use graph to draw my plots with metapost. However, the following minimal file does not work: \usemodule[graph]

\starttext \startMPcode draw begingraph(3in,2in); gdraw "agepop91.d"; endgraph; \stopMPcode \stoptext

The complete output log is available here: http://pastebin.com/zuGaT87W Thank you for your help ! I can generate the proper picture by writing only metapost code such as : input graph

beginfig(0); draw begingraph(3in,2in); gdraw "agepop91.d"; endgraph; endfig; end;