I just upgraded a drupal 6 website to drupal 7 successfully after few upgrade failure.
Preparion before upgrade
– disable all non-core (required/optional) modules.
– switch back the default theme to garland.
– backup the database to sql file.
Migrate and upgrade
– rsync to drupal 7
– change value of $update_free_access to TRUE in settings.php, and change the file all writable.
– goto the /install.php of your drupal site at web browser to upgrade.
Reset the overlay 「Toolbar」 at drupal 7
1. Backup the database to sql file.
2. DELETE FROM menu_links WHERE module = 『system』
3. Then you need to visit /admin/config/development/performance and clear the cache.