[Plugin: Shadowbox JS] IE7 error with YouTube videos

I am seeing an odd problem with only IE7. I am using the shadowbox plugin to display a YouTube video, with the following link:
<a href="https://www.youtube.com/v/tVadzIsYexg&autoplay=1" rel="shadowbox;width=660;height=525" title="Battle with the Bugs">
It works perfectly in FF and IE8, but in IE7 the shadowbox opens but is completely blank, and the browser reports an “object expected” error.
My dev site page is: https://www.gjkrause.com/hbdredo/adventures
clicking on the second image shows the issue in IE7.
Any help is much appreciated!