Trying to get sys working, but below doesn't work (No Userforms here, only WS)

Private Sub Worksheet_Activate()
With ActiveSheet.ComboBox1 ' A Control toolbox type CB
.ListFillRange = Range("Sheetlist") 'SheetList is dynamic range via
=Offset(X,0,0,Counta(A:A),1)
.ListIndex = 0
End With
End Sub

Also tried .Rowsource inplace of ListFillRange, buy NO CIGAR, Why is that?

TIA,,,