I have just recently bought a Roxio Game Capture, and i have to say, it works fine, but i was unable to hear myself in xbl parties and what not. so, i bought a pair of Turtle Beach x21's. pllugged it into my computer for the mic, and the audio, works fine when i test it, when not capturing.
When selecting "Microphone (USB)" which is my headset for the audio to record with, and i can hear ALL the audio (xbox, talking, myself) perfect. BUT, when i hit START CAPTURE, i get the "Unknown Capture Error".