Room Mailbox - Your meeting request was declined

When you reschedule appointments in a roombox you can get this error:

Your meeting request was declined. It didn't specify an end date. The end date must be before x/x/xxxx.

To fix this start the Exchange Management Shell and set this commands:

get-CalendarProcessing * |fl |findstr Roombox set-CalendarProcessing "Roommailbox" -EnforceSchedulingHorizon $false set-CalendarProcessing "Roommailbox" -BookingWindowInDays 1080

After this cmdlet you can schedule the appointments more than the default 180 days.