I have these XY values:
Series S1 = new Series()
S1.Points.AddXY(9, 25);
S1.Points.AddXY(10, 35);
S1.Points.AddXY(11, 15);
chart1.Series.Add(S1);
Curious as to why your range array was sprawled out like that. It would have been cleaner to put your array in brackets as it was defined and also initialized. e.g.
string[] range = new string[10] {"","7-8","8-9","9-10","10-11","11-12","12-1","1-2","2-3",""};
/*
The tenth element is also likely unnecessary
as it simply repeats the first
element of the array
*/