I'm calling the histogram function in VBA code. The
function accepts 3 Range Objects as inputs. Are there
limitation to these objects and or where they reside.

It seems to me, through trial and error, that the range
for the bins (the third range) must be specifies as RANGE
("A1:A24") or that style and not RANGE(Cells(r1,c1), cells
(r2,c2)). The first two ranges will accept the bins to be
defined dynamically.