Thanks for your help Bernie.

You were right. I misplaced my entry. (My status as a novice is
showing.) I tried to reconstruct a bit and enter the macro in
ThisWorkbook but again with no success. Perhaps you can quickly see
the problem. The range is a little different from my original sample
entry, as is the cell with the symbol. If you have a solution, it
would be much appreciated. Thanks again.

Private Sub Workbook_SheetChange(ByVal sh As Object, ByVal Target As
Range)
'MAKE 'X' CHANGE TO 'CHECK MARK' IN EXTBID & INTBID
If Target.Cells.Count 1 Then Exit Sub
If Intersect(Target, Worksheets("ExtBid").Range
("R2:T4,R7:T27,R42:T47")) Is Nothing Then Exit Sub
If Target.Value < "" Then
Application.EnableEvents = False
Worksheets("ExtBid").Range("AA4").Copy Target
Application.EnableEvents = True
End If
End Sub