happens too to me, tried win8.1 64 and win7 pro 64
(windowed mode)
sometimes, i try to hit ctrl-shift-f10 again when the game window is focused. some combination of clicking ok to codec window and this starts unrelieably the recording.
what you mean by suddenly? was it once working (no for me, has been like this forever) ?
edit: fixed keystroke combo -.-
