[NTG-context] "Invalid field" in Mark IV

Dear all, I didn't use ConTeXt for some time and, so, have just re-installed the minimals tonight. When running on some of my files, Mark II does its job well but Mark IV tells me error: Invalid field id nucleus for node type choice (0) . l.133 ... M décrit l'axe $({\rm O};\vect{e_{x}})$ avec une vitesse $\dot{x}... I have absolutely no idea what it is trying to say to me... If related, the macro is defined by \def\vect#1{% \overrightarrow{#1} } Regards, -- Flavien. ---------------------------- "Quantum objects are completely crazy but, at least, they are all crazy in the same way." R.P. Feynman.