Error with sum when variable changes

[Bananas212]

Hi all. I'm having a bit of a problem with the sum function when a locked cell is being summed. The only way I can explain it is to show you with an example. In Cells b3 & b4, you're supposed to be able to change the numbers and have the cells d7-d107 be the cumulative sum of the cells from c7 to c107. It is perfect when cell b3=2, but whenever I change that number it gives me a number error in cells d7-107. Can anyone help please?

[FDibbins]

change the formulas in C to this,...
=IFERROR(COMBIN((B9-1),($B$3-1))*($B$4^$B$3)*((1-$B$4)^(B9-$B$3)),"")
(I changed it in D8, so start there and copy up and down)

The reason D:E are giving errors is because D8 is giving an error, and messing up the =sum()

[Bananas212]

Thank you so much!