[NTG-context] font file size

Hi all, while getting context/luatex to work, I experiment with fonts. I play with DejaVu fonts. I found that when I use DejaVuSerif.ttf I get what I want, but when I use DejaVuSans.ttf context produces nothing. It seems to process document without any error message and gives no pdf. I made some investigation and I guess it has something to do with file size of the font (DejaVuSerif.ttf-242KB, DejaVuSans.ttf-557KB). Result is the same for fonts from collection with similar size. Conversions with fontforge do not help. Is there any limit for size of font? Any other possible reason why? Thanks for suggestions. ZS