Can't select Checkin & Checkout dates in calendar.

I have previous bought booking module Order ID: 16583
and it works perfect on http://www.valsgaardforsamlingshus.dk

Now I have to bought the module to http://www.jans-auto.dk - if else I can get it to work for them
initially, they just want see the module in operation, but I simply can not be allowed to book
anything when I click in the calendar nothing happens.

I have tried to disable Mootools System Update plugin, I have tried to date: http://www.artio.net/support-forums/booking/booking-paid/i-can-not-choose-the-date-on- the-calendar
but nothing helps, and I can not demonstrate the module, the customer wants, of course, not to buy.
Help wanted urgently!

PS. A Danish translation is 95% ready!

Sincerely,
Jens