I joined because I saw a you-tube series ages ago, this was back in the mod. At the time I was too young to join but when SA came out I remembered and decided to join the community.
Make sure you are only placing the last bit of the link into the field not the whole one. Show in blue, if this doesn't solve it it may be something website side rather then a youtube problem. You can also use a mp3 upload site and use it that way too.
www.youtube.com/watch?v=RgKKgzVhMgY