Hi David,
Sorry but the upgrade procedure for MySql changed a little, I changed the readme.txt to indicate the change.
Previously we included the MySql scripts in the MS SQL package, but to make it smaller we no longer do that and the MySql scripts are in the MySql download. You need to copy the contents of the Setup folder in the My Sql download into the /Setup folder of your site, then visit Setup page again.
Best,
Joe