We have a few users in our environment that use Macs and so use Outlook 2011, because of the issue shared calendars have with Outlook 2011 those users use OWA. For some reason when a user creates a new calendar in Outlook 2013 and then shares it will others it can be added through Outlook 2013 or 2010 but cannot be opened through OWA. The error message that is given is something to the effect of "you either do not have permission or the folder no longer exists". The permissions granted by the 2013 user is Editor or something similar and the email will be opened in OWA less than a few minutes after it has been sent. Is this an incompatibility between 2013 and Exchange 2010?