Make Theme: social icons appear only as empty boxes

Hello all,
I use make theme from thethemefoundry
and have this problem:

Since some time the social icons (implemented by make theme, from font awesome)
appear only as grey empty boxes.
both on frontend and in the backend
(in backend you can let the available icons displa, and also there only grey empty boxes)
Can anyone give me a tip on how to let the origina icons display?