You can't view free/busy information on another user's Calendar in Exchange Online

Applies to: Exchange OnlineOutlook 2016Outlook 2019

PROBLEM


You cannot view free/busy information for a specific user in Exchange Online. You experience this issue in Outlook Web App and Microsoft Outlook (including Outlook for Mac 2011). Specifically, you experience the following symptoms:
  • When you try to view the user's Calendar in Outlook, you receive the following error message:
    could not be updated

    Screen shot of the user's Calendar which shows the
  • When you try to view the user's Calendar through Outlook Web App, you see a red triangle with an exclamation mark. 
    Screen shot of the user's Calendar which shows a red triangle with an exclamation mark

CAUSE


This issue occurs if the user's Calendar has a time slot that contains more than 1,000 entries. 

SOLUTION


Delete unwanted items from the user's Calendar so that there are fewer than 1,000 items in that particular time slot.

MORE INFORMATION


To confirm that this is the issue that you're experiencing (if the user is running Outlook 2010 or Outlook 2007), follow these steps:
  1. Enable troubleshooting logging in Outlook. For more info about how to do this, see the following Microsoft Knowledge Base article:
    831053 How to turn on the Enable Mail Logging option for troubleshooting in Outlook
  2. In the %temp%\OLkAS folder, look for the availability service log file that's named <date>-<time>-AS.log or <date>-<time>-fb.log.
  3. Search the log file for an entry that resembles the following:
    <MessageResponseClass="Error"><MessageText>Microsoft.Exchange.InfoWorker.Common.Availability. ResultSetTooBigException: The result set contains too many calendar entries. The allowed size = 1000; the actual size = <xxxx>
    Note the number that's represented by the <xxxx> placeholder. If you're experiencing this issue, this number will be more than 1,000. 
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