I had the same problem on a site of mine just yesterday.
It was a new wordpress site and I assumed that it was something about the theme or the plugins I had installed.
Then today I tried to post a youtube video on a site that has been using Vipers Video Quicktags for years and I got the parsing error.
Strangely, my older Youtube videos are still working. I can see that I have entered the Youtube link correctly.
What could possibly cause this problem only on a NEW post and not on the previous posts using vipers video quicktags?
**Update** -- Ok. A few minutes later and it has started working. It's a mystery to me. So my problem appears to have magically solved itself.