This morning I still had a working instance of MySQL on my Win 7 dev box, as part of a XAMPP installation. Then I decide to try a standalone MySQL; I uninstalled XAMPP, downloaded the MySQL 5.5.17 msi package, and ran it. I have now tried 3 times, the last time after removing all traces of MySQL from my machine, and each time I get the same error.
The installation runs fine, then kicks off the Instance Config Wizard. This runs fine until the "Applying security settings" step, which fails with an "Access denied" error for the root user. It suggests opening 3306 on the firewall, but it has already done this for me.
I have installed MySQL as standalone some time ago without any problem. What could be wrong here?