Sub with ByRef to a Word.Application

[asedt]

I have problem creating a private sub to replace text in a wordfile, is the use of ByRef good? The problem is that this works on my developing computer but not at the target computers.

Private Sub Replace(ByRef WordApp As Word.Application, ByVal OLDText As String, ByVal NEWText As String)
        WordApp.Selection.Find.ClearFormatting()
        WordApp.Selection.Find.Text = OLDText
        WordApp.Selection.Find.Replacement.ClearFormatting  ()
        WordApp.Selection.Find.Replacement.Text = NEWText
        WordApp.Selection.Find.Execute(Replace:=Word.WdRep  lace.wdReplaceAll, Forward:=True, Wrap:=Word.WdFindWrap.wdFindContinue)
    End Sub
 

I get this error message during runtime:

System.NullReferenceException: Object reference not set to an instance of an object.
  at MyProg.Form1.Replace(Application& WordApp, String OLDText, String NEWText)
 

Here is some source code where i create the word object, in my project i have added a reference to Microsoft Word 11 Object Libary, COM.

Dim WDApp As Word.Application
WDApp = CreateObject("Word.Application")
WDApp.Visible = False
 
WDApp.Documents.Add(Template:="C:\template.dot", Visible:=False)
 
Replace(WDApp, "<Replace ME>", "New Text")
 
WDApp.Documents.Item(1).SaveAs("C:\newdoc.doc")
 
WDApp.Quit()
WDApp = Nothing