I think you are getting object reference error because of the path. Please see my example below:
YouTubeRequestSettings settings = new YouTubeRequestSettings("NETUnittests", YTDeveloperKey, YTUser, YTPassword);
settings.Timeout = 10000000;
YouTubeRequest request = new YouTubeRequest(settings);
Google.YouTube.Video video = new Google.YouTube.Video();
//video.VideoId = lblVideoID.Text;
//http://gdata.youtube.com/feeds/api/users/USER_ID/uploads/VIDEO_ID
Uri videoEntryUrl = new Uri("http://gdata.youtube.com/feeds/api/users/default/uploads/" + lblVideoID.Text); video = request.Retrieve<Google.YouTube.Video>(videoEntryUrl);
if (video.ReadOnly == false)
{
}
string tt = video.Title;
string dd = video.Description;
video.Title = tbTitle.Text;
video.Description = tbDescription.Text;
video.Keywords = tbKeywords.Text;
//video.Status.Value = "private";
request.Update(video);