Hi,
You don'the have a single account at Nabble. You have one or more completely independent registrations at different forums at some of which you may be the administrator.
Please go to:
http://support.nabble.com/Invite-Subscribers-Activation-Request-f7589263.html and post your request there. Include the URL of the forum for which you need the invitation facility added.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.