It turns out that YouTube will no longer provide a video's keywords to anyone except the video's owner. I don't know why that is, but I'm including YouTube's documentation after my signature for reference.
So that means we have to remove the "add an edge for each pair of videos tagged with the same keyword" option from the Import from YouTube Video Network dialog box. YouTube won't provide the keywords, so the option is now useless.
We could replace this option with an "add an edge for each pair of videos that have the same
category" option, because a video's category (Tech, HowTo, Education, People, etc.) is public. As someone analyzing YouTube data, would such an option be useful to you?
"Note that a video entry will only include keywords if the API request was authorized by the video's owner. If the API request was not authorized or was authorized by another user, <category> tags containing keywords will not be included in the feed."