I am running a 2010 MS Exchange Server. We recently started sharing calendars accross the domain. The user sharing her calendar is using MS Outlook 2007 and the users having the message "Folder not Available" when they try to open her calendar are also using Outlook 2007. It is only happening to a few users and then sometimes they will try and open the folder again and it will work. I have searched a lot of tech articles and failed to find a reason for this problem. If anyone has an answer to this problem I would greatly appreciate it.