Application problem error:1 Asp.net/VB

  Public wialonurl As String = "http://---------/wialon/ajax.html?svc="

    Public Function getvehicle() As String
        Dim sid As String = Request.QueryString("sid")
        Dim objText As String
        Dim result As String = ""
        Dim url = wialonurl & "core/search_items&params={spec:{itemsType:avl_unit,propName:sys_id,propValueMask:*,sortType:*,propType:*},force:1,flags:0x00000001,from:0,to:0}&sid=" & sid
        Dim req = DirectCast(WebRequest.Create(url), HttpWebRequest)
        Using reader = New StreamReader(req.GetResponse().GetResponseStream())
            objText = reader.ReadToEnd()
        End Using
        If objText.Contains("error") Then
            result = objText
        Else
            Dim json As JObject = DirectCast(JObject.Parse(objText), JObject)
            Dim arrText As String = json("items").ToString()
            result = arrText
        End If
        Return result
    End Function


    Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
        TextBox1.Text = getvehicle()
    End Sub