I've just attempted to upgrade an install of the Drupal 6.10 appliance via apt-get to 6.11. The process appears to work fine, up until the post-installation process.

Despite following the instructions to the letter, running update.php etc, I keep getting the following whenever I try to connect to my site:

Drupal already installed

* To start over, you must empty your existing database.
* To install to a different database, edit the appropriate settings.php file in the sites folder.
* To upgrade an existing installation, proceed to the update script.
* View your existing site.

I run the update script, I click on 'view your existing site' and it loops back to install.php and gives me the above message.

Any ideas?