I am getting this error: “Error during inserting into BD … DB:Duplicate entry NN-NNNN-NN-NN 00:00:00 for key booking_id_dates. How to fix it ?

This issue can happens at the some servers, depend from the configuration of the MySQL at the version 4.0 - 4.0.1 of Booking calendar.

So for fixing this issue, please open the phpMyAdmin or similar tool for the working with DB

and execute this SQL command:

ALTER TABLE bookingdates DROP INDEX booking_id_dates

or this (depend from the prefix at your DB tables):

ALTER TABLE wp_bookingdates DROP INDEX booking_id_dates

then test it again.