Calendar Interop error messages & codes

Here's how to troubleshoot the different error messages you might get when using the Google Calendar Interop tools.

Before you begin

For Google Calendar Interop tools to work correctly, administrators should turn on access to additional services for all organizational units.

  1. Sign in to your Google Admin console.

    Sign in using an account with super administrator privileges (does not end in @gmail.com).

  2. On the Admin console Home page, go to Appsand thenAdditional Google services.
  3. Find Access to additional services without individual control for all organizational units and click Change.
  4. Select ON for everyone, and then click Save.

    Note: Changes might take up to 24 hours to propagate to all users.

If you prefer to turn on access to additional services for specific organizational units only, follow these steps:

  1. Sign in to your Google Admin console.

    Sign in using an account with super administrator privileges (does not end in @gmail.com).

  2. On the Admin console Home page, go to Appsand thenAdditional Google services.
  3. Find Access to additional services without individual control for all organizational units and click Change.
  4. At the left, select the organizational unit.
  5. Select ON.
  6. Click Override to keep your setting if the service for the parent organizational unit is changed.

    Note: Override will overrule the settings inherited from the parent org unit. Changes might take up to 24 hours to propagate to all users.

Learn more about additional Google services and organizational structure.

Error messages & codes

Calendar Interop error messages
Error message Description Recommended action
Connection error

Google Calendar wasn't able to connect to the Microsoft Exchange server. A firewall might be blocking access. Or, you entered the wrong host name or port. For example, you might get this error if your connection to https://exchange.domainname.com/ews/exchange.asmx was unsuccessful.

Use the Microsoft Remote Connectivity Analyzer tool to verify if the Exchange server is reachable from the internet.
Exchange Web Services (EWS) communication error The Exchange server URL is using HTTP rather than HTTPS. HTTP is not a secure protocol. Make sure to specify HTTPS in the Exchange server URL.
EWS response error

Google servers aren’t communicating with EWS, but some other service (for example, a non-Exchange HTTP server).

Common causes of this error include:

  • You entered the wrong URL for the Exchange server.
  • You entered incorrect Exchange credentials.
  • There’s a firewall preventing Calendar from connecting to the EWS server. In this case, make sure the EWS port is accessible from the internet.

In Exchange 2016, to find the correct URL, go to Exchange admin center > servers > virtual directories and then double-click EWS.

For more information, refer to Microsoft Exchange Web Services Connectivity Tests in the Microsoft Remote Connectivity Analyzer tool.

Exchange username is not an
email address

The Exchange username specified in the Admin console is not a valid email address. For example, it might be missing the domain name.

Check the Exchange Role Account to make sure it’s the correct email address.

Host not found

The DNS name is incorrect or misspelled. Or, there’s no DNS record for the specified host name.

Make sure the Exchange URL in the Admin console is correct.

Interop is not set up

No Exchange connection settings were found. Calendar Interop might not be set up in the Google Admin console.

Make sure Calendar Interop is turned on in the Admin console.
Invalid attendee

The user you’re doing an availability lookup for doesn’t exist.

Make sure the user you’re doing the lookup for exists in Microsoft Active Directory.
Malformed Exchange URL

The Admin console doesn’t recognize the Exchange URL. It might be in the wrong format.

Check the settings in the Admin console and make sure the correct URL is entered.
SSL error

This message is the result of one of the following errors:

  • The SSL certificate doesn't match the name of the host you’re trying to connect to. You might have entered an IP address instead of a host name. Or, tried to connect using an alias that’s not recognized by the certificate.
  • The SSL certificate is invalid. The certificate might be expired. Or, it's potentially from an untrusted root Certificate Authority.
Make sure the SSL certificate on the Exchange server is valid and matches the name of the host you’re trying to connect to.
Calendar Interop error codes
Error code & name Description Recommended action
400 Bad Request

Fail to fetch OAuth access token.

Possible causes of this error are:

  • Wrong value used for the Application (client) ID.
Make sure the application ID is correct.
401 Unauthorized

Fail to fetch OAuth access token.

Possible causes of this error are:

  • Wrong value used for the Client secret.
  • An app registration might not have any client secrets associated with it.
  • Your organization’s Access Control List might be preventing the application.
Make sure the client secret is correct and that it’s associated with the correct application.


Google, Google Workspace, and related marks and logos are trademarks of Google LLC. All other company and product names are trademarks of the companies with which they are associated.

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