i have a solution, follow what I say
1.select the video which you want to play,
2.then just type the word "kick" into the address bar just before Youtube,
eg.you have the address "http://www.youtube.com/watch?v=wXLdOw79pcM&feature=topvideos",
instead of this link just type 'kick' in front of youtube and press enter, there will appear a new window with the same video then just click on the download link tour download will be start
there is a other way just go to the video and click to the uploader name and find that video from there and try to download that you must be able to download the video
Here's the easiest proven method to capture those videos that RealPlayer Downloader no longer will download. First, download Youtube Downloader HD (yep, it's free). Run the program, set your default download sites, etc. Next go to the video you are having difficulty with and start to run it. As it's running right click on the video. One of your choices will be "copy video URL at current time". Click on that and paste it into the Video URL space in Youtube Downloader HD. Then on the lower right corner click on Download. Works every time.