已解决，多亏了拉法尔(Rafal)的帖子:

Solved, thanks to Rafal's post:

问题在于，正在创建新MyParticipant的线程被默认设置为MTA，因此在MyParticipant内部，MTA线程正在调用新的VideoRenderer，该继承了Image.构造UI控件的MTA线程会导致此异常.

The problem is that the thread that was creating a new MyParticipant was being default set to MTA, and so inside MyParticipant, that MTA thread was calling new VideoRenderer, which inherits an Image. An MTA thread constructing a UI control results in this exception.