Private Sub Worksheet_Change stops working when I have certain workbooks open.

hi,

I have a large model (45 sheets) , with the following code on one of the sheets

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim KeyCells As Range
    Set KeyCells = Sheets(1).Range("projects")
    
    If Not Application.Intersect(KeyCells, Range(Target.Address)) _
    Is Nothing Then
 
Call Locked
    End If
End Sub

It works fine at the moment with only that workbook open. However, with other workbooks open at the same open its stops working and it does not start working even after I close the other workbooks.

Does anyone have any ideas?