Error code 606 means the code you are entering is invalid. It can be because one digit (or more) is incorrected or you are trying to enter a Code for TurboTax Online in a Desktop software (or vice-versa). The codes for TurboTax Online will not work with TurboTax Desktop & vice-versa.
Please contact TurboTax customer support for further assistance using the following link
TurboTax Phone Number