If your company has Pre-Registration set up you should be able to automatically use Pre-Registration.
If not, please check you have the following in place.
Invite people via Outlook - To invite people via Outlook meetings you need to be on the staff list.
Invite people via VisitorRego Portal - To invite people via the Portal you need to have a login.
If you belong to multiple sites, you will need to select your default site.
This is so your email address can be linked to the site location for Outlook Pre-Registration.
You can technically make invites from any site from the website.