I followed the instructions. I backed up the currently working forum, backed up the DB, then deleted all the files. I uploaded Vanilla 1 ( I previously had the pre-release ver) , went to the url, followed the instructions re chmod, then clicked the appropriate upgrade link. The error message gave as stated above.
If you are upgrading from a pre-release version, you do not need to run the upgrade script. All you need to do is copy the new files on top of the old ones. That's it.
The new files contain an empty conf folder, so your old conf files should remain intact.
The upgrade script is only intended for people who are upgrading from Vanilla 0.9.2.x to Vanilla 1.0.