Been running a WP Multi site with BP installed for quite

Been running a WP Multi site with BP installed for quite a while. I need to run an extra network with a different domain so i installed WP Multi Network Plugin - seems to work so far, allows me to "add" 2nd network and "move" blogs from one to the other.

the 2nd domain I have done all the necessary DNS stuff so currently it "arrives" at my hosted server IP correctly, but just keeps on defaulting to the main site/blog.

I tried using domain mapping plugin, no luck.... only thing i can think of , is that in set up they say remove the following 4 lines from wp config

*****************************************
define( 'DOMAIN_CURRENT_SITE', 'mydomain.com' );
define( 'PATH_CURRENT_SITE', '/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );
*****************************************

PROBLEM is - the moment i do, none of my blogs or sites load - just error saying no WP sites installed or configured at this address