I’m not able to post a youtube video successfully. Tried with the help of Timethief over the New Year’s Eve weekend. She finally had to copy the youtube URL and I copied what she did and transferred it to my post. Then it worked. I had this problem once before and you had to fix the media icon before the youtube transfer could work.
I seem to remember that both times, this and last, I had been previewing themes right before. Could it be that the process of previewing messed up my link icon somehow.