Free/busy was not available in Outlook & OWA for a resource mailbox. Also we were not able to change the calendar permissions for this affected mailbox. This is how I solved this issue: Cause: there was a corrupt item in the Calendar folder in Outlook and the Calendar folder has to be deleted and recreated. Since you cannot delete the default Calendar folder in Outlook you have to do this using MFCMAPI tool (download from http://mfcmapi.codeplex.com/). But first, in Outlook you have to backup all appointments from the default Calendar to any other calendar ( for example, create new Calendar Folder: call it like cal1) Solution: step-by-step - Enable the resource mailbox account in AD, and login as the resource mailbox. - Launch Outlook and disable the cache mode and close and open Outlook. - In Outlook, create a new Calendar folder: cal1 (a new folder with Calendar Items). - Switch the Current View of Calendar & cal1 to All Appointments view - Select All appointments in Calendar, drag them and press Ctl and then drop them to cal1 (pressing Ctl allow you to copy all items rather than move). - Once all appointments get copied to cal1, close Outlook and launch MFCMAPI tool. - Go to Session → Logon and Display Store Table → Select the outlook profile of the resource mailbox → expand Root → Top of Information Store → Right click on the Calendar → Delete Folder → Check Hard Deletion. Once deleted, close MFCMAPI tool. - Open Outlook, and a new Calendar folder will be automatically created. - Finally move all appointments from cal1 back to the Calendar, and delete cal1.