Problems with Youtube downloading

I recently purchased the program, and found it worked very well d/ling several short Youtube videos sequentially entered. In the last few days, however, I receive a message that all videos (save the first of any group) can't be downloaded the first time I try them. I have to remove them from my list, and reenter them to download. This holds true regardless of intensity and connection speed; I've tried a wide variety. Same results. Would appreciate it if you could look into this.