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Upgrading drupal7 problem, role_permission already exists?

trying to upgrade drupal 6 to 7. but when open site.com/update.php, error message as below
http://i.imgur.com/T3sGJ.jpg

below is the step that i use:
1) off-line
2) choose garland theme
3) disable non-core modules
4) remove default.settings.php
5) delete all folder and files excepts sites folder
6) copy all drupal 7 files to directory
7) setting.php permission set 666

nobody click here