Can you specify how you did it using Afterburner? All of mine come out as solid black.
That's exactly what i was experiencing with the 2 programs i tried, as well as the default. The video would lock up for 5-10 seconds why the sound continued, and the screenshot would be solid black.
Maybe its just not possible right now? I've played the game a total of ~2 hours, and the game crashed 3 times while in the menus, on top of the screenshot issue.