Unable to access Domain Mapping menu in Tools

Hi, I have tried multiple attempts and installations to get the Domain Mapping plugin working on my site.

I have followed the directions provided by WPMU Dev as well as checked many posts online.

Everything alright until I want to actually map a domain. Unable to access the 'Domain Mapping' menu item under 'Tools'.

Would someone please give me some insight, am I doing something wrong, have I missed something...

Have had several attempts and followed the directions;
update - site to be MultiSite (have even tried even with pre-install installation through Softalicious)
update - wpconfig.php
update - .htaccess

I have a dedicated IP, and SSL. Have tried installation with two different domain names. Any help would be greatly appreciated...

Thank you in advance.

PS - I have successfully activated and used the other WordPress MU Domain Mapping plugin for another site... am just having issues with this version of the plugin.