Since Exchange Resource Manager uses the calendar of the resource rather than the published free/busy information when processing meeting requests, meeting requests sent to resources that appear available may be declined if the free/busy information has not had a chance to replicate. The advantage of this approach is that double-bookings do not occur when resources are managed by ERM.
One potential solution to this issue is to request a meeting with the required resource first – once the meeting is accepted by the resource the organizer can update the meeting and add attendees, etc. This will guarantee that the resource is available at the time the request is sent to other invitees.
As far as the best method for picking a resource from available free busy information, that’s a matter of personal preference. I like to use the Group Schedule functionality of Outlook 2002 to see the published free/busy information for all our resources at once. The “Plan a Meeting” option can also be used to make a selection based on the currently published free/busy information as well.