The Item With the Specified Name Wasn't Found

I am getting run-time error '-2147024809 (80070057)' The Item with the specified name wasn't found. The debug highlights the "Chart 1" row in the code below. I would be very grateful to anyone who can help me resolve this issue. The strange thing is, my macros seem to run for the most part, but this error pops up when I first open the file, or when I make any kind of changes to line items in my Excel schedules. Thanks for your help.

----------------------------------------------------------------

Option Explicit
Private Sub Worksheet_Calculate()

Dim KeyCells As Range

' The variable KeyCells contains the cells that will
' cause the following macro to run when they are changed.
Set KeyCells = Range("g37")

' Place the rest of your macro code below.

ActiveSheet.ChartObjects("Chart 1").Visible = KeyCells = 1
ActiveSheet.ChartObjects("Chart 2").Visible = KeyCells = 2
ActiveSheet.ChartObjects("Chart 3").Visible = KeyCells = 3

End Sub

That did the trick...many thanks!