Users receive an - One or more of your reminders could not be snoozed or dismissed - error when they dismiss or snooze calendar reminders, how can I fix this?

There are two possible causes for the “One or more of your reminders could not be snoozed or dismissed” error:
  1. The SystemAttendantDN registry key may be missing.

    Solution    : To add the SystemAttendantDN registry key, refer to Microsoft KB 3104440
  2. The value of the user object attribute legacyExchangeDN is incorrect. 

    Solution: Follow Microsoft KB 556073     to correct the legacyExchangeDN attribute value for affected users. The Global Address Book should be rebuilt after updating the attribute.

    NOTE: The Outlook AutoComplete function may continue to use the incorrect legacyExchangeDN value; add the “incorrect” value to the affected user’s proxyAddresses attribute to ensure email delivery.