@Arthur81 I just took another look at your listing's calendar and it seems that you have a reservation now for October 14 so the problem might have been from the guest's end (payment issue or ID verification issue). Or, have you changed anything in your Availabilty settings?
I also noticed that your last review was in June. Did you Unlist your listing for some period of time? If that is the case, then the guest might have tried to book before your listing became fully "re-listed" again on Airbnb's database. The reason I say that is because sometimes listings appear in search when they are not fully ready to be booked and guests get the error message you described. This happens most often with new listings.
So, it seems that all is well now, right?
Clare