To start, these are NOT set up as true room/resource accounts. These are user accounts, with other users set up as delegates.
All accounts were able to be booked as resources by all users when we were on Exchange 2007. We completed moving all but a few accounts over to Exchange 2010 in the past couple of weeks.
The problems started for the few users once the accounts were moved to Exchange 2010.
These particular users do not seem to be able to book any of the various "room" accounts around campus as a resource, they always get the same error message, regardless of their level of permissions to the room. On some of the rooms they have author level, others reviewer level, and on some no specific permissions.
The majority of users are able to book these same accounts as resources just fine, including those having no specific level of calendar permissions to the accounts. This only seems to be about 10 users out of 1500+ that can not.
Further complicating the process is that it appears to be very much Outlook client driven. If any of the users having the problem logs into Outlook Web App, they can book those same accounts as resources just fine.
In Outlook, if they simply list the account in the To: line, and forgo booking the account as the room, the appointment works fine as well.
All accounts in question are on the Exchange 2010 servers now.
We do have public folders set up on Exchange 2010 as we still have a few lingering accounts that are still using Outlook 2003 that we have not been able to upgrade yet, and had to provide free/busy access for them.
Have ran through the reported "fixes" noted on other threads from un-checking cached mode or checking it, making sure public folders are mounted, and making sure the auto configure is pointing to the Exchange 2010 CAS servers, all appears to be in order.