After about 10 charitable mileage data entries, the 11th would not calculate when the mileage was entered in the "Miles per trip" cell and the "Once" checked.  Rather, the "Miles Driven" cell remains yellow shade and unpopulated, unlike all the previous entries which calculate and change to no shading.  Further, the "Total Donated Value" cell remains blank, unlike the other entries which are properly populated.  I tried removing the entry - but the reference number will not delete.