Problem uploading fontello custom icons

I have a problem adding fontello custom icons
page url : http://www.hattusas.it
wp version 3.8.1
enfold version 2.4.5

when i click in general settings “upload/select fontello font zip” it show me the “Upload file screen”, and then the media library, but when i select the file and click on “insert zip file” return me this error :

“couldn’t add the font
the script returned the following error :
(empty space)”

empty space means that there is no description of the error

is there a way to manually add the icons via ftp?

thank you
P.S.