I feel like I am going round in circles here chasing your messages. You don't need to send me private email AND write the same thing on the forums.
Like I said in my reply to your private email, this message doesn't come from the HotPot module. It is a message from your browser, telling you that an XML file has invalid syntax. After Googling for the message - have you tried Googling for the message? - I saw that this message can be caused by many things including something as appararently trivial as empty blank lines at the beginning of an XML file.
You do not say what kind of video you are trying to insert or how you are trying to insert it, neither do you say what kind of Hot Potatoes exercise you are using nor do you tell us what settings you are using for the HotPot activity, but from the very limited information you have given, I would guess that you need to look at any XML files associated with the video.