First, just wanted to say that this is my favorite cap software ever, but I am getting the exact same A/V that is being reported above. It seems to happen for me after screencap has been running for a bit. I try to do a region cap, and the A/V pops up. If I stop the program and then start it up again, I can capture stuff again. I don't really know what the timeframe is, though.
Some extra information that might help, I run Emerge Desktop as my desktop.