Add guest isn't linked

Hi,
I’ve just installed the plugin and it seems to work great so far, except one problem. I have Additional Guest’s turned on and the green + button appears at the bottom of the form but it isn’t clickable. I’ve looked at the source code and it doesn’t appear to have a link attached to it.

Has anybody else found this same problem? If so, how should I look at correcting it?

Many thanks.

http://wordpress.org/plugins/rsvp/