Is there a reason line 4a on the tax return would be different than the 1099R summary?

I have entered 5 1099R's with a total gross distribution of $103,043.  This is the amount that shows on the 1099R Summary.  However, on line 4a of the tax return, it shows a total of $99,371.  Also, the total taxable amount on these 1099R's is $59,543. but the amount on 4b of the tax return shows $57,476.  Why are the amount different?