Yes, when I exported they were joined together as per the video instructions. Anyway, I gave it another shot uploading to IMVU with the same file I used last night and, inexplicably, this time it worked. I wish I had an explanation for why the animation wasn't working the first time, but I really don't know. Perhaps a restart of IMVU was all that was needed.
In any case, it was a good learning experience since it forced me to go back through the video to make sure I had done things correctly and to reinforce my understanding. Thank you very much for posting the video and for your help!