SOURCE http://support.microsoft.com/kb/2836889/en-us
When you use Microsoft Office Outlook 2007 to share your calendar, you receive the following error message:
Error while preparing to send sharing message.
You receive this error message only when you use Outlook 2007 and connect to a Microsoft Exchange Server 2013 mailbox or a Microsoft Exchange Online mailbox.
Also, if you try to check the permissions on the calendar, you may receive the following error message:
An error occurred when setting schedule permissions.
Workaround
To work around this issue, do one of the following:
- Use Outlook Web App to share the calendar or to set up calendar permissions. For more information about how to do this, see the following Microsoft resources:Users who are running Microsoft Outlook 2013, Outlook 2010, or Outlook 2007 can directly accept sharing requests and invitations that are sent from Outlook Web App.
- Use a computer that has Outlook 2013 or Outlook 2010 installed to create a temporary Outlook profile. After the profile is set up, you can use Outlook 2013 or Outlook 2010 to send calendar sharing requests and to edit calendar permissions.
For more information, go to the following Microsoft websites:- Outlook 2013: Video: Share your calendar
- Outlook 2010: Video: Share your Office 365 calendar
http://office.microsoft.com/en-us/web-apps-help/sharing-your-calendar-HA103842904.aspx#_Toc342645965