It's doubtful that TurboTax is making any error with respect to this entry. Why do you think there is an error?
A distribution from an inherited 401(k) will include code 4 in box 7 and will not have the IRA/SEP/SIMPLE box marked.
In general, the amount from box 1 of the Form 1099-R should be included on Form 1040 line 5a and the taxable amount from box 2a should be included on line 5b. If the problem is that TurboTax is generating a penalty for failure to complete the entire RMD for the inherited account, make sure that when entering this Form 1099-R that you indicate as the required RMD only the amount of RMD for this inherited account.
