I just upgraded from 6.02.08 to 09 and every time I load the page, it just goes back to the upgrade wizard. The upgrade says it works fine, but then when I click click here to access your site, it just takes me back to the upgrade wizard.
If I change auto-update to false, then I get the under construction page.
The usual reason for this behavior is difficulty connecting to the database. Check the connection string in web.config.