[solved] Update from 6.31 to 6.33: "undefined function: _system_theme_data()"

Hi all,

Well, I am stucked for some days now with an upgrade from 6.31 to 6.32, and now 6.33.

I followed the advices from upgrade.txt:

1. Backup : done
2. User id#1: done
3. Off-line mode: done
4. Bluemarine theme: done
5. All modules disabled: done
6. Remove old files & directories (except site/): done
7. Unpack new structure: done
8. Copy special files (htaccess in my case): done
9. Verify configuration: done
10. Run update.php: wrong

As soon as I reach this last step, I have got an update.php?op=info page with (when commenting the ini_set('display_errors', FALSE); line in the update.php file):
Fatal error: Call to undefined function: _system_theme_data() in /home/associattl/www/includes/theme.inc on line 493
I basically see what mean this error (can't find the function... even if everyting seems in place :-/ ), but how to fix it ?

Any help would be welcome!