Do you experienced a situation whereby you only see a broken camera icon next to your display picture whenever you tried to initiate a Video Call session with others? Or others can see you but you can't see your ownself in your webcam? Apparently it is a bug in Windows Live Messenger but not in MSN Messenger v8.1 or previous version of it.
If that is the problem, there's a viable workaround for it.
Link : http://messengergeek.spaces.live.com/blog/cns!E3785B1281BBDA1!3016.entry
Link (Discussion, another method to use if the previous one failed) : http://www.ariam.co.il/forum/forum_posts.asp?TID=82&PN=1