​ErrorCalendarInvalidTimeZone: ​Calendar items cannot be processed because your client access Exchange server is missing a definition for the reference UTC / GMT time zone.


To verify if the UTC / GMT time zone is missing using OWA:

  1. Open OWA (Outlook Web Access) for any mailbox
  2. Go to Options (right hand corner)
  3. Select Regional Settings
  4. Expand the Current Time Zone combobox
  5. Check if (GMT) Coordinated Universal Time is present (see attachment)
  6. Cancel changes (only check if the time zone is defined - do not change it)

To verify if the UTC/ GMT time zone is missing using the Windows registry:

  1. Login to the Exchange Server(s) providing client access
  2. Start regedit
  3. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones
  4. Check if a UTC registry sub-key is present (see attachment)​

Once you have verified the problem, ensure the reference UTC/GMT timezone is defined on your Exchange server.

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