Plugin not working properly

I have installed the Appointment + plugin, when I look at the front end as a customer, I can see the current month's availability (December 2012), when I click on the "Next Month" button, I get February, NOT January as it should be. I tested this in November and the same thing happened. Every time I hit the "Next Month" button, a month is skipped between current and next. URL for my appt scheduler: http://www.99dollarscarpetcleaning.com/schedule-your-service/

Thanks for your feedback on this..