VB.Net & Delphi

This is the code I use in the VB.net, but it never give me problem. It runs concurrent with Java Applet, the problem is the Delphi application that give the error. I have no the Delphi code but I had a look on it and it use low level access to the file ...

    Private Function cercabanconote() As Boolean
        Dim swok As Boolean = True
        valore = 0
        Try
            If File.Exists(BILLS_FILENAME) Then
                Try
                    Dim sr As StreamReader = New StreamReader(BILLS_FILENAME)
                    valore = sr.ReadLine
                    sr.Close()
                Catch ex As Exception
                    Setlog("BILLS_FILENAME->" + ex.Message)
                    MsgBox(ex.Message, MsgBoxStyle.Critical, "BILLS_FILENAME")
                    valore = 0
                    swok = False
                End Try
                If valore > 0 Then
                    Try
                        Dim sw As StreamWriter = New StreamWriter(BILLS_FILENAME)
                        sw.Write("0")
                        sw.Close()
                    Catch ex As Exception
                        MsgBox(ex.Message, MsgBoxStyle.Critical, "BILLS_FILENAME")
                        Setlog("billsfilename->" + ex.Message)
                        valore = 0
                        swok = False
                    End Try
                End If
            End If
        Catch ex As Exception
            Setlog("File.Exists->" + ex.Message)
            MsgBox(ex.Message, MsgBoxStyle.Critical, "File.Exists")
        End Try
        If valore > 0 Then
            Setlog("caricati ->" + valore.ToString)
        End If
        Return swok
    End Function