Loop opening workbooks run-time error '9' on workbook variable

Public myfilename As String
Public locn As String
Public contact As String
Public mypath As String
Public subject1 As String
Public signature As String








Sub mgmtrefresh()


    Dim ws As Worksheet
    Dim mgmtwb As Workbook
    Dim wb1 As String
    'Dim myfilename As String
    'Dim locn As String


wb1 = ThisWorkbook.Name
Workbooks(wb1).Activate




    
With Application
    .Calculation = xlCalculationManual
    .ScreenUpdating = False
    .EnableEvents = False
    .DisplayAlerts = False
End With




'START LOOP


'Set Counter (Do Until # should be set as Counter for last item on Locs List + 1)


    Sheets("Mapper").Activate
    Set counter = Range("Counter")
    Range("Counter").Value = Range("startcounter") 'cell f2
    
Do Until counter = Range("endcounter") 'cell g2
    
     
Worksheets("Mapper").Calculate
 
    mypath = Range("mypath")
    myfilename = Range("myfilename")
    locn = Range("locn")
    path = Range("path")
    contact = Range("contact")
    subject1 = Range("subject1")
    signature = Range("signature")
        
'Open individul file template


Workbooks.Open mypath, UpdateLinks:=1
'Set mgmtwb = Workbooks.Open(mypath)
    
With Application
    .Calculation = xlCalculationManual
    .ScreenUpdating = False
    .EnableEvents = False
    .DisplayAlerts = False
End With


 


' Select Individual template


   Workbooks(myfilename).Activate
 


'Individual template
    Application.DisplayAlerts = False
    Application.Calculate
'   Workbooks(myfilename).RefreshAll
    ActiveWorkbook.UpdateLink Name:=ActiveWorkbook.LinkSources, Type:=xlExcelLinks
'   ActiveWorkbook.UpdateLink Name:=ActiveWorkbook.LinkSources
'    Worksheets("Mapper").Calculate
'   Worksheets("High Level").Calculate
    Application.Calculate


   
'Call mgmtemails




Workbooks(myfilename).Close SaveChanges:=True
 ' ActiveWorkbook.Save
' ActiveWorkbook.Close
  
  
  
  
    Application.DisplayAlerts = True
    
'Activate main macro
   Workbooks(wb1).Activate
   
    Application.CutCopyMode = False
    
    Sheets("Mapper").Activate
    Range("Counter").Value = counter + 1
    


'END LOOP
    Loop
'Load timestamps
'Call LastFileDateTime_MgmtReports
           
'Save mapper file
   Workbooks(wb1).Saved = True
   
    
With Application
    .Calculation = xlCalculationManual
    .ScreenUpdating = True
    .EnableEvents = True
    .DisplayAlerts = True
End With
    
End Sub