Thanks for your answers fellas!
@Fubar2Niner: that GUI looks awesome! but i just cant get it to work. Tried running the game as admin, changing the resolution on the d3d.cfg file... nothing. it just CTDs on start.
@Mittelwaechter: I disabled the d3d fix, and taking screenshots worked as expected. So its confirmed, it is the resolution fix that is causing the problem.
Seems i now have to choose, crappy pixelated graphics to take screenshots of, or not taking screenshots of the nice graphics.