We are using Exchange Server 2007 SP1 Rollup 6. When Entourage Web Services (EWS 13.0.7) or Outlook 2011 for Mac is used to change permissions on a person's calendar the Read attribute is being changed from "Full Details" to "None" behind the scenes. The effect is that free/busy information is blocked for any person or group that is listed on the person's calendar. This has been a known issue that MS has not acknowledged as far as I know. The following blog article describes it fairly well at: Calendar Sharing Permissions Bug in Entourage Web Services: http://blogs.utexas.edu/glenmark/2010/02/26/calendar-sharing-permissions-bug-in-entourage-web-services/ Possible related to this Read: None issue is another anomaly on the PC side with Outlook 2007 or Outlook 2010 : I've discovered (rediscovered?) that Outlook 2007 will display "Custom" just after the user selects "Contributor" for a person's calendar permission level. I've confirmed that this behaves the same for both Outlook 2007 and Outlook 2010 clients. Try this in Outlook 2007 or Outlook 2010. See if you can grant someone Contributor access to your calendar. On the Mac side, the user can using EWS or Outlook 2011 to set the Read attribute to "None". However; on the PC side, the "None" option is grayed out in the Read section. On the Mac side, the selections of "None | Free/busy time | Free/busy time, subject, location | Contributor" all work and display properly. Any of the higher permission levels (Reviewer, Author, Editor, Owner) are associated with the Read attribute being set to "Full details" and display as "Custom" in Outlook for Windows (whereas they appear to be correct to the Mac user). The Mac Web Services client appears to be taking some action that causes the Read attribute to be set to "None" when displayed in Outlook for Windows. Everything looks fine when viewed from the Mac client. There also seems to be a mutually exclusive relationship between "Folder visible" and "None" on the Mac client. Uncheck the attribute "Folder visible" will change Read to "None". Changing Read to "None" will uncheck "Folder visible". The PC client does NOT allow the None option in the Read permission section to be selected (grayed out). From the blog, there are indications from Cornell that SP3 for Exchange 2007 has fixed this issue. Has anyone experienced these issues with Exchange Server 2007 Rollup 4 and/or can confirm that SP3 addresses this buggy interaction between Web Services clients and Exchange 2007. Thanks, Bill