KB Article: http://support.microsoft.com/kb/982774

INTRODUCTION

When you send a meeting request in Microsoft Office Outlook 2010 to a mailbox that is configured for direct booking, the meeting is not successfully booked. You do not receive an error message in this scenario. If you open the mailbox that is configured for direct booking, the meeting request is in the Inbox folder.

Note When earlier versions of Outlook successfully book a meeting together with a mailbox that is configured for direct booking, a meeting request is never sent to the resource mailbox. Therefore, a meeting request in the Inbox of the resource mailbox indicates that the meeting was not successfully booked.