I am trying to convert the .doc file into .txt from Access. File convert one by one works fine but when i try to convert a bunch of file, it gives syntax error "Invalid Procedure call or argument" but it convert one file.

Error Line
sFile = Dir

Public Sub DocToTxt(ByVal sDocTxtFile As String, ByVal sTxtFile As String)
Dim wdApp As Object
Set wdApp = CreateObject("Word.Application")
If Dir$(sTxtFile) <> "" Then Kill sTxtFile
wdApp.Documents.Open sDocTxtFile
' wdApp.ActiveDocument.SaveAs sTxtFile, 2, False, "", False, "", False, False, False, False, False, 1252, False, False, 0, False
wdApp.ActiveDocument.SaveAs sTxtFile, 2
Set wdApp = Nothing
End Sub

Button in form
Private Sub Command43_Click()
sFile = Dir$("S:\Shared Services\PPVTEST\*.doc")
Do While sFile <> ""
sFile = LCase$(sFile)
DocToTxt "S:\Shared Services\PPVTEST\" & sFile, "S:\Shared Services\PPVTEST\" & Replace(sFile, ".doc", ".txt")
sFile = Dir

'DocToTxt "C:\PPVTest\findings.doc", "c:\PPVTest\f.txt"
End Sub