Exact same thing happens to me. I am using Apple Mail (not Gmail), and Apple's Calendar, and iCloud; no Enterprise server on my end. Late 2011 MacBook Pro with latest software updates, iPad 2 with latest software, and iPhone 5S with latest software.
When someone using Outlook sends me a modification of an existing shared meeting they originally created, trying to accept the update generates the error message. The options, of course, are "revert to server," which leaves you with the original, unmodified, appointment; "try again," which gives you the same error message again immediately, and "ignore," which gives you a brief bit of time where you think the issue is solved by an over-ride, but then, alas, the error message pops back up.
So, let's try to be clever and accept the update on one of my other devices, shall we? On my iPhone and iPad, I cannot even open the e-mail attachment containing the appointment - the attached appointment blinks, indicating that I did, in fact, click on it and try to open it, but nothing happens. Nothing at all. On my iOS devices, in Settings, under Mail, Contacts, and Calendars, I have "Shared Calendar Alerts" set to "on," which is supposed to notify "about new, modified, or deleted shared events." But, not so much in my case.
This happens whether the person who originally created the shared appointment, and who is sending the modification, has an Enterprise server, or not. I spent some time in an online chat (about half an hour) then on the phone (another half an hour or so) with Apple yesterday about this. I even directed them to this conversation. In the end, all they could recommend at this point was for me to :
- Go into System Preferences, under "iCloud," and uncheck "Calendars."
- Close Calendar
- Reopen Calendar
- Close Calendar again
- Go back into System Preferences, under "iCloud," and re-check "Calendars" to let it re-establish my calendar with iCloud.
So I've tried that, and the calendar is re-establishing itself in the cloud now. I'll see if that fixes the issue. They are aware of the issue, though, and seem to be working on it.
The issue seems to be related to permissions or access to the pre-established iCloud shared calendar item - part of the error message (on my machine, at least) indicates that access to the the specific calendar item is not permitted. However, I walked through some of that with Apple, and they seemed to think that since I can access iCloud from my side, and establish my own calendar invitations, based on what info they had, that it shouldn't be a function of something on my computer not being set correctly.
Also, I think that under similar circumstances, if the sender doesn't try to move the DATE of the appointment, but instead just modifies the contents - like updates a conference call-in number or something, I don't THINK I get the error message, but the updated content never takes, either. I haven't had this happen in a while, and haven't had someone try it to see if my memory is correct, but I think that's the case. I may need to go try that to see what happens.
Maybe the OS update corrects the issue for Gmail, but I'm not using Gmail. Maybe my re-establishing my iCloud account will help my issue; or the update will help with Apple Mail, too. If not, maybe they are working on it and a fix will be forthcoming, but I'd rather not have to go through the machinations I've seen here and elsewhere to fix the issue, or write some Apple Script thing to deal with it as I've also seen suggested - I assume this a "relatively simple" (easy for me to say!) programming issue that can be addressed.
And as long as we're on Calendar-Outlook-Shared Appointments, here's another, semi-related issue - when someone with Outlook sends me a shared appointment invitation to an appointment that they have created on their calendar as an "all day" appointment (i.e., appears only at the top of their calendar, not blocking out the whole day as a "timed" event) when I accept that on my MacBook Pro, or my iPhone, or my iPad, rather than getting imported as an "all day" event, it shows up as a timed event blocking out from midnight to midnight. I am unable to modify the invitation or the appointment so that it resides at the top of my calendar - the "all day" box is grayed out; I assume this is because I am not the creator of the appointment. So something is lost in translation there, too. So far, I have noticed this happening when the sender is using an Enterprise server; I don't know if the same problem occurs when there is not an Enterprise server in the mix.
