Windows Forms program runs smoth on win7 but on previous os's give the "Index was outside the bounds of the array" Error?

Question

I have a Windows Forms program that runs smooth on win7 but on previous version of windows give the "Index was outside the bounds of the array" error in the imageList call when setting the key-image of the component.

Why this can be hapening?

PS: This only occur when running the .exe, not when debugging.