Windows 7: Windows Live Messenger Microphone Issue

I've been trying to configure Windows Live Messenger for video chat and I'm encountering a completely inexplicable issue.

My microphone works perfectly; but Messenger seems unwilling to detect it in video chat. The person on the other end receives my video feed but no audio. I can receive both his video and audio correctly.



I've tried video chat with a couple of different people and neither one can hear me. What's even stranger, though, is that if I record a self-contained "video message" and play it back, I can hear my own audio perfectly (so clearly the mic is working and clearly Messenger can interface with it). But if I send that prerecorded video with working audio to another person, it doesn't always play properly on his end. One person gets a working message with both video and audio. The other person gets video only with (as in video chat) no audio.

I've checked every Messenger option and mic setting I can find and nothing seems relevant. The mic seems to be working perfectly and (as demonstrated when I record video messages) Messenger is able to "hear" it. It simply won't work in video chat, and even prerecorded messages don't always have audible sound.