On the off chance that this post is found by some poor sucker who has the same problem, here's what I did:
1. At command line, enter command "mysql --host <your backend host> --user mythtv --password mythconverg"
2. When prompted for password, enter your mythtv database password (probably "mythtv")
3. At mysql command line, enter command "delete from videometadatagenre;" (do not forget the semicolon!)
4. At mysql command line, enter command "delete from videometadatacountry;"
5. At mysql command line, enter "\q" and hit return to exit mysql.