Users Registering w/o Invite Code

CM Vers. 2.2
WP Vers. 3.5.2

Despite having the CM Invitation Code plugin installed, I am still receiving numerous registrations from users without invite codes ???

Is there a way that I can set the system (my site) to prevent this?

lcag.info

TIA for your time, effort and consideration.

~Respect

http://ww.wp.xz.cn/extend/plugins/cm-invitation-codes/