Hi,
It looks to me like your code (if it worked as written) would simply be testing to see if the change happened within the range A1:A100, and if so, make the cell in column B equal to the cell that got changed in column A. (yes?)
If that's correct then you don't need to assign variables and loop through the range, we can do it with just this one liner:
Code:
Private Sub Worksheet_Change(ByVal Target As Range)
If Not Intersect(Target, Range("A1:A100")) Is Nothing Then _
Target(, 2).Value = Target.Value
End Sub
If this is not your intent then can you post back with what is?
Oh, and one question, are the values in column A getting changed manually, or are they formulas that are updating?