Issue:

Resource mailboxes configured for direct booking aren’t automatically accepting meetings

Cause:

Direct Booking has been deprecated in Outlook 2013 – Changes in Office 2013

Resolution:

Convert the (resource) mailbox from user to a room mailbox.

Useful resources:

How to Convert a Mailbox ?

http://technet.microsoft.com/en-us/library/bb201749(v=exchg.80).aspx

How to Enable or Disable Automatic Booking on a Resource Mailbox

http://technet.microsoft.com/en-us/library/bb123495(v=EXCHG.80).aspx

How to Upgrade Outlook Direct Booking Resource Mailboxes to Exchange 2007

http://technet.microsoft.com/en-us/library/bb232195(v=EXCHG.80).aspx

Thanks & Regards

Rahul Thomas