Why is 5b wrong? It should be the taxable amount of 5a. Is it too low or too high? Delete that 1099R and re enter it.
FYI - If you edit or review a 1099R it does not keep your answers from before but resets them to the defaults. Then you have to go through and answer them all again. So be sure to go all the way to the end of the 1099R section. They are right unless you go back.