You entered an invitee that wasn't recognized by the server

I installed Sierra (10.12) few days ago an began getting a similar calendar error, "You entered a group that wasn't recognized by the server." This is a personal calendar so an iCloud server issue (vs Exchange). The options are 'remove group' and 'edit event' neither of which deliver any action i.e., they don't work. APPLE, what is going on here??

I'm getting the same error. I edited the event (there were no invitees listed) and the error persisted. I deleted the calendar entry on the Exchange server and iCal still reports the error. Now when the error pops up and I try to edit the event there's nothing to edit. It's frustrating, but not enough to make me switch to Outlook for Mac!

We're running Exchange 2010 SP1 on the backend.

iCal 4.0.4 (1395.7), Mac OS/X (10.6.7)

I have the same exact problem, it is not happening on my primary Exchange calendar but on our teams calendar, so I have to turn it offline in iCal preferences and switch it back on if I'm to view it. It's pretty frustrating and hasn't changed from Lion Beta until now.. Any help anybody?

Deleting and reconnecting the calendar doesn't work.

hmm - i'd forgotten about this issue until your note popped up. i'm no longer having the problem, but i don't know when it stopped. i'll check through the logs and see if i can find the last occurrence. the only thing that's changed since may is that i'm now running 10.6.8

Hi,

I am running Lion 10.7.1, but I have this issue long before switching from OS X 10.6.5 I think. It has to do something with the exchange server and recurring events, as the other events do not pop up as errorneous.

I have this problem too

I can't find another thread that has an answer, and this one hasn't been active for some time. Did anyone find a fix? We have a serparate shared calendar from our Exchange server, I get the same issues as listed by everyone above.

I am still having this problem even with Mountain Lion. It gets pretty serious because the consequence is that somehow many copies of the same meeting invitation email is generated and stored on the draft folder of my exchange server. Seems it becomes more of a problem when more than one of my Mac's are online and seems to only happen to events that are created by my delegate. The message pops up the moment I click "close" on the reminder of the event and then this crazy message about invitee not recognized by the server pops up (and drafts of the invitation from myself to myself appears in the draft folder).

Someone else out there must be experiencing this as well, anyone know of a solution?

Thanks.

Bump. Wake up Apple. Provide a solution please!!!

Can't believe there aren't more people experiencing this problem. My situation can't be that unique, either that or there is setup issue with my Exchange server. I am getting hunders of draft emails created in my server draft folder which I have to clean once in a while, what a pain!

This happens to me, too. When I go to edit the event, there are NO invitees listed, making it impossible for me to correct. The alert keeps popping up, over and over and over.

I am experiencing this issue as well. I am starting to wonder if it has something to do with using a local account on the mac versus a domain account?