Code D would not be present on a Form 1099-R that reports a distribution from an IRA.
TurboTax would determine an excess accumulation if the amount that you indicate as the RMD for the inherited IRA is more than the amount distributed from this inherited IRA. Editing the 1099-R or deleting the 1099-R from TurboTax and reentering it, paying special attention to answering the RMD question correctly, should correct the problem.
