SUM OFFSET Issues

Hey Guys,

I am Trying to implement the Depreciation solution described in link below, SUM(OFFSET

http://www.sumwise.com/blog/straight-line-depreciation/

But if No of Years is pushed to 7 or more the formula fails, I need it go work up till 30, Can anyone help me Fix the formula

Thanks in Advance

If I add 30 columns in the beginning, it seems to work ...... anyone have better solution ?