No longer able to use Youtube URL in survey...?

I've been working on a survey for about a week now, and have had a Youtube video embedded in multiple questions for most of that time--no problems. I recently realized that I'll actually have to use a different video, so I removed the old one and plugged in the URL for the new one (using the "Rich Content Editor" tab), but it says that it's "not a supported media type." What's really weird, though, is that I then tried to plug the old video's URL back in, trying to figure out what the difference is, and now it won't accept that one either. Ideas?