[NTG-context] Dimensions of a picture

I have a problem with the following fie : \useexternalfigure[fig1][Mouette1]%1600x1200 \useexternalfigure[fig2][Mouette2]%1024x768 \starttext %the following line gives an error : %Error: pdfetex.exe (file ./Mouette1.jpg): reading JPEG image failed %\externalfigure[fig1] %the following lines runs very well \page \externalfigure[fig2] \stoptext Is there a limitation of the dimensions of a picture ? Or another problem ? Thank you