A common cause for this error is that the target user being migrated is currently suspended within the G Suite tenant account. If the user has been suspended, we recommend that you restore the suspended user, and try the migration again.
Read the Restore a suspended user article from Google for more information on how to restore a suspended user within a G Suite environment. Note: Once a user is restored, it can take up to one hour for the changes to take effect.
Make sure that the user is subscribed to the Calendar service, as this error can also be caused by the user not being subscribed. For more information, see Turn Calendar on or off for users.