Connections

I am trying to use TeamViewer to help my Nana with her new tablet. We both have TeamViewer installed on our devices (her tablet and my laptop); however when I enter her Teamviewer ID into my system, a notification pops up that says: "This ID is unable to accept invitations." I don't exactly know what this means, but I want to get this working so I can help her out.

Thanks in advance!