Problems with room booking

When I try to set a recursive appointment with my team, booking a room for it, I experience a problem.

Outlook add the room among the participants but it doesn't book it, so it seems everythnig ok but the room is not booked.

It happens for example that I set 18 occurrences, putlook advice me that the room is available for 14 occurences on 18, I receive 4 email stating that it is not possible to book that room but I don't receive the 14 confirmation and the room is not booked.

The same if the room is available for all the 18 occurences. No confirmation email, no booked room.