This error code is shown after selecting "Transfer Your User Data" when you log in to a Nintendo Account for which transfers are not possible.(* 1)
In order to transfer your user data, first check the Nintendo Account that's linked to the user on the source console.
After you've confirmed the account, start the user transfer process again. When you reach the Nintendo Account login, make sure you log in to the Nintendo Account that's linked to the user you're transferring.