Multisite Setup - Multi DB & Pro Site

Good day,

I'm looking to run a small version of wordpress/edublogs:

1) I have made a fresh WP install
2) I then activated Network install
3) Successfully installed Multi-DB

The problem now is that I cannot access my wp-admin to install SITE-PRO and Domain-Mapping... my domain takes me to:

http://mydomain.com/wp-signup.php?new=mydomain.com
......... there is no such page....

I have a feeling I should've activated the SITE-Pro plugin before multi DB...?!?

Can anyone assist?

Thank you
Whoweez