Make sure that you are not entering a "0" in the box for 9A.  Even if your 1099-R form has a zero, you should leave that entry blank.  TurboTax will read the zero as a value and will produce an error because it wants a value at least 0.01%.  This is true of most entries in TurboTax - it is a best practice to leave boxes blank if they are zeroes unless the entry specifically says to enter a zero.