I assume that by "long-standing" you mean that you had the Roth 401(k) for more than 5 years. Were you also over age 59½ at the time of the distribution from the Roth 401(K)?
Did you do a direct rollover from the Roth 401(k) and received a code H Form 1099-R for the rollover to the Roth IRA? Does the Form 1099-R from the 401(k) show an amount in box 5?
What is the code in box 7 of the Form 1099-R for the distribution from the Roth IRA?
Assuming you were under age 59½ and had no other money in Roth IRAs, the amount in excess of what you contributed to the Roth 401(k) would be taxable and subject to a 10% early-distribution penalty. The amount of your contributions to the Roth 401(k) should be present in box 5 of the Form 1099-R. TurboTax should pick this amount up and treat it as contribution basis in your Roth IRAs, but sometimes it seems that that doesn't happen and you need to enter it manually. Make sure that you have clicked the Continue button on the Your 1099-R Entries page and have addressed all of the questions there.
