That error only occurs if you already ran the uninstall script and are trying to uninstall again. You need to check your logs for the original error that halted your first uninstall attempt. Like I do every time someone reports uninstall problems, I have uninstalled a default installation of VaultWiki Lite, and again I have encountered no problems. It's possible you can encounter issues if:
1. You had an older version of VaultWiki Lite installed
2. Upload the new version because you wish to upgrade
3. Forget to run the upgrade script
4. See errors on your site due to #3
5. Attempt to uninstall VaultWiki Lite
6. The uninstall fails because you are using the uninstall file for a version that you don't currently have installed, because of #3
7. Database is corrupted and you are unable to uninstall or reinstall VaultWiki Lite
The only way to correct this problem is to open the vault/tools/uninstall.php file and look at the code for a list of changes it would make to your database. Using phpmyadmin or a similar server admin tool, manually make the changes. Only if ALL changes are made properly will you be able to successfully reinstall VaultWiki Lite (or VaultWiki, for that matter).