Gideros Font Creator export blank problem

whidbey

I use "Gideros Font Creator",import the font from windows/fonts/arial.ttf,
and export font to "arial.png".
it will generate 2 files: arial.png and arial.txt
aria.txt is fine,but arial.png shows blank when preview.

what's the problem?thank you in advance.

whidbey

by the way,I use "Font" class instead of "BMFont",then the charecters will appears.
is there different between "font" and "bmfont"?