Mpost disabled?

[Herv� Rouault]

Hi!   I always have my problem with mpost (MiKTeX 2.1, ConTeXt 2.5). When I try to compile a ppchtex file I get :   -Randomizer initialized to 1493581758. -system(mpost -progname=mpost -mem=metafun glucose-mpgraph)...disabled. - - -figures        : figure glucose-mpgraph can not be found       Mpost seems to be disabled, where can I enable it?   Herv�