Mac users can't make appointments in the room calendar

Hi,

Our Mac users can't make booking in the room calendar in Office 2011, the item doesn't display on the calendar and no error message show up. However, if I setup the users on Outlook in Windows, then they are able to book and show on the room calendar.

I setup the room permissions for 

Default - Author

Anonymous - Author

my self - Editor

I update the Mac OS and Outlook 2011 already, it is still the same.

I am pretty sure we can do this before, it just happens recently. Is there something wrong on the exchange server? Please advise. Thanks