Since 18.0.93 or 94 (I think it was 93) and the release of the new YouTube format, I frequently get a Failed (9) error when trying to download YouTube Videos. When this happens the download progress box in the corner indicates immediate 100% success (attachment 1) but nothing is downloaded. The download details screen is mostly blank with only basic info like the name and a Status of Failed (9) (attachment 2). This happens perhaps 40-70% of the time and I haven't discerned any patterns. Repeatedly attempting the download has ultimately worked, although I've gotten up to 11 clicks (waiting a second or two to confirm that the download failed before retrying). I initially rotated through the various links for each video (Thumbnail, title, etc.) but simply clicking on the same link repeatedly seems to work too. It happens with both the IE and Chromium browser engine settings.
This led me to realize that I can't do anything with a failed download. I would expect the option to try again. However, I have to go back and find the video again through the web page.