[NTG-context] Metapost code does not work - Can you find the problem?

Can someone please tell me why the code below does not work? Thanks a ton. \starttext \startuseMPgraphic[CS] u:=1cm; pickup pencircle scaled 2pt; %Paths path demandCS; demandCS := (0,5u) -- (10u,0); % Draw Demand draw demandCS withcolor 0.5red; % The point on demand curve draw ((6,2) -- (6,0)) scaled u dashed evenly withpen pencircle scaled 1pt withcolor 0.5white; draw ((6,2) -- (0,2)) scaled u dashed evenly withpen pencircle scaled 1pt withcolor 0.5white; \stopuseMPgraphic \useMPgraphic{CS} \placefigure[here][CS1]{Consumer Surplus}{\useMPgraphic{CS}} \stoptext