multisite_manager site with same database

After reading all kinds of stuff about multisite. I have installed multisite_manager I am using that, trying to add a site to same database as the root site.

Rood/main Dupal domain: http://alanya-guide.dk
Drupal Site domain: http://tni.dk

I run my Drupal at a well reccomended danish Drupal hositng called GIGAHOST, here I redirected the domain tni.dk to the main domain alanya-guide.dk.

My procedure as sugested:
Created folder in Sites for my new site called tni.dk via FTP.

Create content - Drupal Site - and filled in Title and Shortname, next under Advanced I filled in http://tni.dk - {shortname}_ I leaved as is, and that was it. When I clicked Save, 15 errors occur (have tried deleting the site and recreating with same result): Warning: Table 'malmskov_drupal01.TNI_watchdog' doesn't exist query: INSERT INTO TNI_watchdog (uid.......... Here I provide a screendump of how I filled in the form: http://n7.dk/TNI_Drupal_Site_Rediger_screendump.jpg
When I refreshed the page the errors dissapeared, but further testing showed the site did not work:

With standard settings.php in new site folder: When I browse the new site I get install procedure asking for a database.

With main settings.php in new site folder: When I browse the new site I get the content of the main domain.

Hard to understand that multisite is so difficult when other Drupal work seems so well checked. But I am aware that this multisite_manager module (http://drupal.org/project/multisite_manager) is alpha1 stage.

Any help is very appreciated. Really need to get the new site up and running.