That's odd. I think what may have happed is that the output window has been resized (somehow) to a size larger than your screen. Can you try clicking (i.e. don't double-click it) on it and dragging it to the left and see if you're able to get to one side of it (you may need to click and drag to the left to move it multiple times). If not, you can delete the file at ~/Library/Preferences/com.inklen.MixEmergency and this will reset all of your MixEmergency preferences and window positions.
