Deleted

If this is the first year of withdrawal,

the contributions previously taxed by NJ  must be zero.

@shadowfx 

You shouldn't delete your question, it may help other NJ tax filers.

In fact, the contributions previouly taxed can be greater than zero if this is the first time you are using NJ Worksheet C,

which is actually the question.

The TurboTax phrasing is misleading,

In the case of a properly executed tax-free backdoor Roth contribution, that can't happen.