How to resolve runtime error '50290': Method 'Quit' of object '_Application' failed ?

type ClassModule  [CExcelMonitor (Code)]
----------------------------------------------------------------------
Option Compare Database
Private wbk As Excel.Workbook
Private WithEvents app As Excel.Application
Private mstrFilePath As String
Private blnKillFile As Boolean
 
Public Property Set MonitoredWorkbook(wbkIn As Excel.Workbook)
   Set wbk = wbkIn
   Set app = wbk.Application
   mstrFilePath = wbkIn.FullName
End Property
 
Private Sub app_WorkbookBeforeClose(ByVal Wb As Workbook, Cancel As Boolean)
   If Wb.FullName = wbk.FullName Then
      app.EnableEvents = False
      app.Visible = False
      AppActivate "Microsoft Access"
      If MsgBox("Do you wish to keep a copy of the workbook?", vbQuestion + vbYesNo, _
                           "Keep workbook?") = vbNo Then
         blnKillFile = True
         wbk.Close False
         Kill mstrFilePath
      Else
         wbk.Close True
      End If
      app.Visible = True
      app.EnableEvents = True
   End If
   app.Quit         <----------------- Breakpoint 
End Sub
------------------------------------------------------------------------
 
Dim clsMonitor As CExcelMonitor
 
Private Sub UDLSummaryByBranch()
                  
    str_sql1 = "If  Exists(SELECT * FROM dbo.SYSOBJECTS WHERE NAME = 'tblUDLSummary' AND TYPE = 'U') DELETE FROM tblUDLSummary"
    DoCmd.RunSQL (str_sql1)
                   
    Set com = New ADODB.Command
    With com
       .CommandType = adCmdStoredProc
       .CommandText = "dbo.procUDLSummaryByBranch"
       .ActiveConnection = CurrentProject.Connection
       Set rstQueryFS = .Execute
    End With
        
    ExportedFile = strAccessPath0 & strAccessPath7 & "SUMMARY_BY_BRANCH" & "_" & intYearSP & "_" & Format(Now, "mmddhhnnss") & ".XLS"
         
    DoCmd.TransferSpreadsheet acExport, 8, "tblUDLSummary", ExportedFile, True, ""
    Beep
    MsgBox "Summary By Branch records have been exported to Excel", vbOKOnly, ""
    If isFileExist(ExportedFile) Then StartDocACS ExportedFile
    DoCmd.Hourglass False
End Sub
 
Private Sub StartDocACS(filename)
 Dim xlApp As Excel.Application
 Dim xlWB As Excel.Workbook
 Dim xlWS As Excel.Worksheet
 'open excel template
 Set xlApp = New Excel.Application
 xlApp.Visible = True
 Set xlWB = xlApp.Workbooks.Open(filename)
 Set clsMonitor = New CExcelMonitor
 Set clsMonitor.MonitoredWorkbook = xlWB
 Set xlWS = xlWB.Worksheets(1)
 xlWS.Columns.AutoFit
 xlApp.ScreenUpdating = True
End Sub