Calendar can't decline the event "(null)" on the exchange server

You need to reset your calendar, to revert to the echange server version.

From the properties

- memorize your current settings,

- then remove the culprit calendar,

- restart the calendar app,

- then add it back and wait for the sync,

- verify that the error is gone.

Thanks trump deck. I have one question - in Mavericks, I tried to remove the account from Calendar but it gave me the message "The Calendar account “asolmssen” is shared by other applications on this Mac. You can remove this account in Internet Accounts." I removed it in Internet accounts and restarted Calendar, but when I added it back in, everything appeared instantly, including the error. It didn't actually re-download anthing. Any suggestions on how to actually get rid of the calendar? Do I have to delete the entire Exchange account and re-import (ugh) my 17GB mailbox?

I solved this problem by entirely removing the exchange account and then adding it back. From settings, internet accounts, highlight the exchange account and click "-". This will remove all mail, contacts and calendar entries. After it finished deleting, re add it. Make sure you have all the settings before you do this. Will take a few minutes to reload everything but then everything worked for me. Only took 5 minutes.

I have deleted the exchange account, twice but the error continues to appear. The creation of the new exchange account takes around 12 hours in my case since I have more than 40,000 emails. Beware.

Thanks, this worked for me (removed Exchange account completely from Internet Accounts, added it back in again). I was getting the error "there was an error trying to send your changes to exchange server" having tried to delete a recurring event in my Calendar - and also a lot of related drafts appearing in my Mail app - but this seems to have cleared it out.

Similar to GianLuca33, I would really want to fix this error without deleting and re-synchronizing gigabytes of data.

(In addition to tens of thousands of mails, I have many folders in Apple Mail, the configuration of which may not survive the procedure.)

I would really like to see a proper fix from Apple.

(I think the error was caused by connectivity problems when deleting an event during a workshop with strange Wi-Fi.)

There was a flaw in my thinking: In Apple Mail, there is no "folder configuration" data which could get lost. (Contrary to some other email clients which I use, e.g. KMail on Linux, where you can configure additional properties that are not stored on the server side.)

So I also went the hard route and removed the account, then re-configured it. Note that disabling the calendar in the account settings does not fix the problem at all (also not in conjunction with restarting iCal or OS X).

Furthermore, I unsuccessfully tried to remove the files responsible for this. I found that ~/Library/Calendars is the correct location, that one needs to look for folders with the .exchange extensions (if there are several ones, one may look inside the Info.plist for the display name), but even completely removing these folders would not help: The information is kept in the "Calendar Cache" (SQLite) database, and if one (re)moves that one, the complete configuration / calendar list is lost, even if one keeps the folders. Thus, if nobody finds out how to modify the database in order to get rid of the faulty entries (which would be Apple's job), I don't see any other easy way out than the ugly solution pointed out several times above.

The problem is that the faulty entry obviously aborts / blocks further synchronization, so I did miss some appointment because it would not show up in my calendar due to the sync problems (displayed also with the "bolt" icon).

Deleting and reconfiguring the exchange account has had some positive effects for me, but not this one. What I no wdo is login to OWA (the browser version of exchange) and delete the event there. then I don't get the null error. It's not perfect, but takes less time than searching unsuccessfully for a solution within Mac's calender.

same problem here, tried removing calendar, caches, etc nothing works

I had a number of problems with iCal, including this one (see my previous post about OWA work around). A major contributor to solving the problems has been to delete my icloud account. The first Account in order is used for the address by ical to determine the return sender. In old iCal versions evidently one could change the order or the accounts so that the exchange address was first. Now icloud forces itself to pole position. Deleting and recreating it makes no difference. At the moment, my iCal problems seem to have gone aaway since making this change.

Deleting the Calendar Cache worked for me. /Library/Calendar/Calendar\ Cache

The null error has not returned and all of the items that were waiting to sync came through.

I had tried to uncheck Cal in my account and rechecking, with and without restart of Cal and OS. This did not work. I did not need to remove and reinstall the entire exchange account.

deleting Calandar Cache worked for me.

http://kb.mit.edu/confluence/pages/viewpage.action?pageId=12386508

deleting Calandar Cache worked for me.

"http://kb.mit.edu/confluence/pages/viewpage.action?pageId=12386508"

This advice helps me! Thanks a lot!