When attempting to book appointments to resource mailboxes, Appointments will appear as tentative, however will not auto accept.
The Auto-Accept Configuration appears to be correct.
Target Exchange environment is 2010
The Mailboxes drafts folder did not synchronize over properly.
Log into each room mailbox with Outlook, which re-initializises the drafts folder. Then restart the MS Exchange Mailbox Assistants service and then everything should start working.
For More information on Configuring Auto Accept, See http://technet.microsoft.com/en-us/library/bb124374.aspx