Guys,
I have same issue and the way to fix it is as someone mentioned above – removing Second <category> tag.
I think it comes from post being part of 2 or more different categories and plugin simply picks it up. Shrt term solution:
Manually fix errors Webmaster tools points out – they actually give you exact line number and re-submit.
Long term – don’t place a blog post containing video into more then One category and you should be fine.