[NTG-context] PNG file corrupted by ASCII conversion

Hi I'm getting the following error with PNG images: libpng error: PNG file corrupted by ASCII conversion !LuaTeX error: libpng: internal error ==> Fatal error occurred, no output PDF file produced! minimal example --- \starttext \placefigure{}{\externalfigure[mill.png]} \stoptext --- LuaTeX in minimals beta-0.70.1-2011051923 (rev 4277) and latest trunk beta-0.71.0-2011061600 (rev 4301) are both affected. Adam