This happened to me last year, and I took it back to Costco. They gave me a new license. They said they don't normally do this, but I have been a long term Costco customer without issue, so they did replace it.
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.
Contact TurboTax Customer support for additional support
I bought my turbotax at Walmart and I am entering the licence code I received in the package and I have checked it 3 or 4 times to make sure it is entered correctly, what should I do !!