Option Explicit

Sub Control_XL()
Dim xlApp As Excel.Application
Dim xlBook As Excel.Workbook
Dim bXLRunning As Boolean
Dim stMainWbook As String

stMainWbook = "C:\Test.xls"

On Error Resume Next
Set xlApp = GetObject(, "Excel.Application")

If Err Then
   bXLRunning = True
   Set xlApp = New Excel.Application
End If

On Error GoTo Err_Handler

Set xlBook = xlApp.Workbooks.Open(FileName:=stMainWbook)

If bXLRunning Then
  xlApp.Quit
End If

Set xlBook = Nothing
Set xlApp = Nothing
Exit Sub

Err_Handler:
   MsgBox stMainWbook & " caused a problem. " & Err.Description, vbCritical, _
           "Error: " & Err.Number
   If bXLRunning Then
       xlApp.Quit
   End If
End Sub