I suggest that you delete the 1099-R and make sure that 4d is cleared and not coming from somewhere else. The re-enter the 1099-R. Box 1 should have the amount if distribution, box 2a must be zero and code 6 in box 7.
Since a code 6 cannot be converted to a Roth and the TurboTax 1099-R interview will not ask about a Roth at all for a code 6 did you change the code to something else? Perhaps you have a 2nd 1099-R with a different code?
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
