Run-time error '1004' when executing Exit Sub command line

Run-time error '1004' when executing Exit Sub command line:

The following code is run from a master workbook. It opens 4 other workbooks and exit. It does what it is supposed to do, but when it gets to the “Exit Sub” command line, it gives an error message of “Run-time error ‘1004’:
Activate method of Range class failed.” 4 times.

Could you please assist in solving this error?
Best regards,
Henk Stander

Sub OpenContractorScoreCardWorkbooks()
Dim PathFabrication As String
Dim FileNameFabrication As String
Dim PathMachineAndValveShop As String
Dim FileNameMachineAndValveShop As String
Dim PathRiggersAndCranes As String
Dim FileNameRiggersAndCranes As String
Dim PathServices As String
Dim FileNameServices As String
Dim MasterFile As String
Dim wb As Workbook, strName As String, strPath As String

' Run the Error handler "ErrHandler" when an error occurs.
  On Error GoTo Errhandler

MasterFile = ThisWorkbook.Name

Application.ScreenUpdating = True

Range("A1").Activate

Range("P3") = "BUSY OPENING WORKBOOKS - PLEASE WAIT!"

Application.ScreenUpdating = False
        
  PathFabrication = Range("I5").Value
  FileNameFabrication = Range("B5").Value
  
  PathMachineAndValveShop = Range("I12").Value
  FileNameMachineAndValveShop = Range("B12").Value

  PathRiggersAndCranes = Range("I19").Value
  FileNameRiggersAndCranes = Range("B19").Value
  
  PathServices = Range("I26").Value
  FileNameServices = Range("B26").Value

    If Not IsWbOpen(FileNameFabrication) Then
       'Test if directory or file exists:
        If FileOrDirExists(PathFabrication & FileNameFabrication) Then
           Workbooks.Open FileName:=PathFabrication & FileNameFabrication
        Else: End If
    End If
          
    If Not IsWbOpen(FileNameMachineAndValveShop) Then
       'Test if directory or file exists:
        If FileOrDirExists(PathFabrication & FileNameFabrication) Then
           Workbooks.Open FileName:=PathMachineAndValveShop & FileNameMachineAndValveShop
        Else: End If
    End If
     
    If Not IsWbOpen(FileNameRiggersAndCranes) Then
       'Test if directory or file exists:
        If FileOrDirExists(PathFabrication & FileNameFabrication) Then
           Workbooks.Open FileName:=PathRiggersAndCranes & FileNameRiggersAndCranes
        Else: End If
    End If
     
    If Not IsWbOpen(FileNameServices) Then
       'Test if directory or file exists:
        If FileOrDirExists(PathFabrication & FileNameFabrication) Then
           Workbooks.Open FileName:=PathServices & FileNameServices
       Else: End If
    End If
        
  Windows(MasterFile).Activate
  
    Range("P3") = ""
    Range("A1").Select

Application.ScreenUpdating = True

Exit Sub		‘THE ERROR OCCURS WHEN EXECUTING THIS LINE

Errhandler:

     'If an error occurs, display a message and end the macro:
      MsgBox Err & ": " & Error(Err) & "  error has occurred, macro execution is terminated."
     
      Range("P3") = ""
      
Application.ScreenUpdating = True

End Sub