CAPTCHA gem

while i am using captcha GEM to get for CAPTCHA images.
i give the font path as where the font file is available.
But at the time of execution i got the error as
" could not open/find font "

and also at default it considered that font path as
/usr/share/fonts/truetype
and after accessing the font path given in captcha.it combined the name
as
/usr/share/fonts/truetype//E:/fontfolder/fonts/arial.ttf.ttf.

For waht reason i got this error.