Hello,
sorry for the delay but solution is in the related topic:
www.artio.net/support-forums/booking/cus...rt/error-2-1-0#40212
You must always update Book it from Book it backend update (if you have inserted your download ID, it is easiest way of upgrading). You had probably updated from Joomla update. It override files, but do not touch database and if there were db changes, it will fail since you try use badly updated component. Booking never delete your data, they are safe. Please run SQL queries from related topic, it should solve problems.
If not, try manually change your version of the component ( file administrator/components/com_booking/booking.xml line 10 ) to <version>2.0.7</version> and update again to the newest from Book it back end updater.