Macro For Selective Data Validation - Which Does Not Work

lately I have promised to program a little macro which looked easy for me to do but on which I have now spend a considerable amount of time without finding the problem why it is not running. I am working under Windows XP with Excel 2010, here is what i was trying to do:

In a worksheet there are two columns G and H. In both columns it shall be possible to select a number of possible entries from a list. For column G this is done via data validation, no problem. Now, the choices which are there in column H shall depend on the entries made in the appropriate row of column G. Column G thus functions as an overarching category. If I choose "Tree" in G, H would give me branches, leaves, apples. If I choose "car" the choices would be wheel, engine, gasoline etc. This shall be done by a Macro:

Code:

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim cat1 As Range
Dim cat2 As Range
Dim x As Integer
Set cat1 = Range("G:G") 'Task Group
Set cat2 = Range("H:H") 'Task Category

[code].....

When running, it gives me Run time error 1004: Method "Range" of object '_Worksheet' failed. Debug highlights the row

Code:

With Range(Cells(ActiveCell.Row, 8))