Appointment + Plugin not working without login (have checked configuration)

Hi there, I have configured the plugin to be used on the site, and its working great apart from one thing that could be a deal breaker! I hope you can help me get to the bottom of this.

The plugin is located on this page: http://aucklandflightpathtrial.co.nz/appointment

Infact I have only three days that I need to schedule for:

http://aucklandflightpathtrial.co.nz/appointment/?wcalendar=1404172800#app_schedule

Anyway - the plugin only works when you're logged into the site - eventhough I've configured it to work without a login. Can you please advise how to get this working without a login?

Thanks,

Rohan