[NTG-context] problem with mp-form.mp while updating minimals

Hi all, I'm updating my ConTeXt (minimals) installation (on Linux-64) and get this error: (/home/jelle/context/tex/texmf-context/metapost/context/base/mp-form.mp ! I can't find file `string'. l.81 input string Please type another input file name: Eventually I did Ctrl-C, but both ConTeXt and MetaPost seem to work, so... (I also installed the minimals from scratch, but get the same error.) Jelle